U.S. patent application number 16/546001 was filed with the patent office on 2020-02-20 for trinuclear gold(i) chemosensor for metal ion detection.
This patent application is currently assigned to University of North Texas. The applicant listed for this patent is University of North Texas. Invention is credited to Sreekar Babu Marpu, Mohammad A. Omary.
Application Number | 20200055876 16/546001 |
Document ID | / |
Family ID | 69523718 |
Filed Date | 2020-02-20 |
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United States Patent
Application |
20200055876 |
Kind Code |
A1 |
Omary; Mohammad A. ; et
al. |
February 20, 2020 |
TRINUCLEAR GOLD(I) CHEMOSENSOR FOR METAL ION DETECTION
Abstract
A phosphorescent chemosensor based on A Gold(I) complex
stabilized in an aqueous polymer media. The complex exhibits strong
red emission (.lamda..sub.max .about.690 nm) in solutions and is
sensitive to sub-ppm/nM levels of silver ions. On addition of
silver salt to the polymer-complex, a bright-green emissive adduct
with peak maximum within 475-515 nm is developed. The silver adduct
exhibits a four-fold increase in quantum yield (0.19.+-.0.02)
compared to polymer-complex alone (0.05.+-.0.01), along with a
corresponding increase in phosphorescence lifetime. The
polymer-complex also exhibits sensitivity to higher concentrations
(e.g., >1 mM) of other metal ions such as Tl.sup.+, Pb.sup.2+,
and Gd.sup.3+. The sensing methodology is simple, fast, and
convenient, and the results can be detected by the naked eye.
Addition of EDTA restores the red emission of the complex. The
complex can distinguish between silver ions and silver
nanoparticles and can be used to remediate silver ions from the
environment.
Inventors: |
Omary; Mohammad A.; (Denton,
TX) ; Marpu; Sreekar Babu; (Denton, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of North Texas |
Denton |
TX |
US |
|
|
Assignee: |
University of North Texas
Denton
TX
|
Family ID: |
69523718 |
Appl. No.: |
16/546001 |
Filed: |
August 20, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62719777 |
Aug 20, 2018 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 21/78 20130101;
G01N 2021/7786 20130101; G01N 31/22 20130101; B82Y 30/00 20130101;
C07F 1/005 20130101; G01N 21/76 20130101; G01N 21/6428
20130101 |
International
Class: |
C07F 1/00 20060101
C07F001/00; G01N 21/76 20060101 G01N021/76; G01N 21/78 20060101
G01N021/78 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] This invention was made with government support under Grant
No. CHE-1413641 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A trinuclear Au(I) complex of Formula I: ##STR00006## or an ion
thereof; wherein: R.sup.1 is --CO.sub.2H, or branched or unbranched
--(C.sub.1-C.sub.6)alkyl-CO.sub.2H; and R.sup.2 is H, halo,
branched or unbranched --(C.sub.1-C.sub.6)alkyl, or aryl; wherein
--(C.sub.1-C.sub.6)alkyl and aryl are optionally substituted.
2. The complex of claim 1 wherein R.sup.1 is --CO.sub.2H and
R.sup.2 is branched or unbranched --(C.sub.1-C.sub.6)alkyl.
3. A chemosensor composition comprising: a) a cyclic gold(I)
trimer; b) a nitrogen heterocycle having a carboxylic acid
substituent; and c) a polysaccharide in aqueous media at a pH of
about the pKa of the polysaccharide; wherein the gold(I) trimer and
the heterocycle form a complex via N--Au--N coordinate covalent
bonds, and the composition is phosphorescent, exhibits a red
emission at about the pKa of the polysaccharide, and has a Stokes
shift of at least about 150 nm.
4. The chemosensor of claim 3 wherein the heterocycle is a pyrazole
or a pyridazine.
5. The chemosensor of claim 3 wherein the polysaccharide is a
glycosaminoglycan or chitosan.
6. The chemosensor of claim 3 wherein the amount of the
polysaccharide in aqueous media is about 0.05% wt/v to about 5%
wt/v.
7. The chemosensor of claim 3 wherein the red emission is at a
wavelength of about 650 nm to about 750 nm, the Stokes shift is
about 200 nm to about 500 nm, or a combination thereof.
8. The chemosensor of claim 3 wherein the pH is about 6.0 to about
7.5.
9. The chemosensor of claim 3 wherein the chemosensor has a
phosphorescence quantum yield of about 5% or greater and a
phosphorescence lifetime of about 3 microseconds or greater.
10. The chemosensor of claim 3 wherein the complex comprises
Formula I: ##STR00007## or an ion thereof, wherein: R.sup.1 is
--CO.sub.2H, or branched or unbranched
--(C.sub.1-C.sub.6)alkyl-CO.sub.2H; and R.sup.2 is H, halo,
branched or unbranched --(C.sub.1-C.sub.6)alkyl, or aryl; wherein
--(C.sub.1-C.sub.6)alkyl and aryl are optionally substituted.
11. The chemosensor of claim 10 wherein the complex comprising
Formula I is a complex comprising X: ##STR00008## or an ion
thereof.
12. The chemosensor of claim 10 wherein the complex is stabilized
by the polysaccharide, wherein the polysaccharide comprises amine
substituents, and the complex is stabilized via ion pairing of a
carboxylic acid group R.sup.1 of Formula I and an amino group of
the polysaccharide.
13. The chemosensor of claim 12 wherein the stabilized complex has
a surface charge that is reduced by about 5 mV to about 20 mV
relative to a non-stabilized complex of Formula I.
14. The chemosensor of claim 12 wherein the composition is
photostable wherein about 4 hours of UV irradiation of the
composition results in less than 10% photobleaching.
15. A composition comprising the trinuclear Au(I) complex according
to claim 1 and a metal ion wherein the metal ion is sandwiched by
two complexes to form a sandwich complex.
16. A method of chemosensing metal ions comprising: a) contacting a
sample comprising metal ions with the chemosensor composition
according to claim 3, wherein the chemosensor composition forms
phosphorescent adducts with the metal ions; and b) sensing the
emission color of the phosphorescent adducts; wherein the metal
ions are sensed via a difference in the emission color of the
chemosensor composition and the phosphorescent adducts.
17. The method of claim 16 wherein the emission peak of the
phosphorescent adducts is blue shifted.
18. The method of claim 16 wherein the metal ions are silver,
thallium, lead, or gadolinium.
19. The method of claim 16 wherein the emission intensity of the
phosphorescent adducts is at least about 5 times greater than the
emission intensity of the chemosensor composition of claim 3.
20. A method of sensing a presence or absence of silver ions in a
sample comprising: a) contacting a sample with the chemosensor
composition according to claim 3 to form a mixture, wherein the
chemosensor composition forms a phosphorescent adduct with a silver
ion when the sample comprises silver ions; and b) sensing the
emission color of the mixture; wherein a presence of silver ions in
the sample is sensed via a difference in the emission color of the
chemosensor composition and the mixture when the concentration of
silver ions in the sample is above about 5 ppb; and wherein an
absence of silver ions in the sample is sensed via no essential
difference in the emission color of the chemosensor composition and
the mixture when the concentration of silver ions in the sample is
below about 5 ppb.
21. The method of claim 20 wherein a green emissive adduct
indicates a concentration of silver ions of at least 5 ppb.
22. The method of claim 20 wherein the sample comprises silver
nanoparticles; and wherein the chemosensor composition is
insensitive to zero-valent silver (Ag.sup.0).
Description
RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn.
119(e) to U.S. Provisional Patent Application No. 62/719,777 filed
Aug. 20, 2018, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] Luminescent sensors for the detection of external stimuli
such as heavy metal ions, pH, and CO.sub.2 have been receiving
significant attention for many years. Silver ion sensing, in
particular, has received immense attention, due to their wide use
in the pharmaceutical industry, electronics, food preservation, and
other industrial consumer products. Silver ions can also accumulate
and cause environmental toxic effects to humans and aquatic
animals. Several research groups have investigated fluorescent
chemical sensors for the detection of various heavy transition
metal ions, such as Hg.sup.2+, Pb.sup.2+, Ag.sup.+, Cu.sup.2+, and
Zn.sup.2+. Generally, such sensors are based on fluorescence
quenching, enhancement, or wavelength change. Compared to organic
fluorophores, transition metal-based phosphorescent complexes have
a plethora of unique and advantageous photophysical properties such
as higher quantum yields, longer lifetimes, larger Stokes' shift,
and higher sensitivity and/or selectivity to local
environments.
[0004] Only a limited amount of literature is available for the
detection of silver ions using fluorescence methods in aqueous or
biological media. Among them, Chatergee et al. demonstrated silver
ion detection using a fluorogenic rhodamine derivative. Arulraj et
al. (Sensing and Bio-Sensing Research. 2015, 6, 19) have reported
the sensing of silver ions using the organic molecule thionine as a
fluorescent probe. Sharma et al., (Eur. J. Inorg. Chem. 2014, 31,
5424) have demonstrated silver sensing using a fluorescent organic
nanoparticle system. Lastly, Schmittel et al., (Inorg. Chem. 2007,
46, 9139) has reported an Iridium-based crown ether complex for
detection of silver ions in MeCN/H.sub.2O system. Thus, it appears,
this is the only demonstration of silver sensing employing a
heavy-metal-based chemosensor in aqueous medium. Additionally, the
generation of the chemosensor is very straightforward and single
step process vs multistep in the literature. Also, the fact that
the chemosensor will detect the free silver ions within a
nanosilver media. Therefore, given the fact that nanosilver is
inducing toxicity concerns for the environment and with limited
investigations existing in aqueous solutions, new materials or
technologies for detecting silver ions are very significant. Also,
it was found that the above-described literature fails to comment
on reversibility or recoverability of the sensors. More
importantly, all of these systems are fluorescent based with no
reports on changes in the lifetime of the sensors relative to
differentiating the presence vs absence of silver ions.
Additionally, it has been found that one of the largest sources of
silver contamination is from engineered silver nanoparticles also
referred to as nanosilver. In the last decade, many commercial
products including toothpastes, bandages, deodorants, kitchen
utensils, beddings, paints, etc. have been loaded with nanosilver
for its strong antibacterial properties. This poses a strong
toxicity and environmental concerns to both researchers and general
public. Understanding the exact mechanism of toxicity of nanosilver
is very challenging due to dynamic morphological and chemical
changes of nanosilver in contact with biological media or the
environment. Ability to sense free silver ions and differentiating
them within nanosilver is one important step in the right
direction.
[0005] Phosphorescent Au(I) complexes including the cyclic
trinuclear (aka "trimer" or "cyclotrimer") complexes represented
herein possess rich intramolecular/intermolecular Au . . . Au
(aurophilic) interactions. Such aurophilic interactions have been
shown to cause striking luminescence properties arising from a
variety of (supra)molecular arrangements of Au(I) complexes and
have been attributed to correlation and relativistic effects. The
rich photophysical properties arising from these effects can be
tuned by altering the size and type of the ligand, nature of the
media, pH, solvent, and by the addition of metal cations or
aromatic molecules.
[0006] The problem is there are a limited number of practical
solutions for the detection of metals such as silver using
chemosensors. Currently a combination of techniques are available
to quantify silver ions in solution, however the leaching of silver
ions from nanosilver cannot be detected or quantified without
sacrificing the sample, a major hindrance for understanding the
toxicity role of different silver species in biological systems.
Accordingly, there is a need for a highly sensitive chemosensor
that can visually indicate the presence of a metal such as silver
at very low concentrations in various media and even in presence of
nanosilver.
SUMMARY
[0007] Herein is reported a phosphorescent chemosensor based on a
trinuclear Au(I) pyrazolate complex or
[Au(3-CH.sub.3,5-COOH)Pz].sub.3, (aka Au.sub.3Pz.sub.3) stabilized
in aqueous chitosan (CS) polymer media. Au.sub.3Pz.sub.3 is
synthesized in situ within aqueous CS media at pH .about.6.5 and
room temperature (RT). Au.sub.3Pz.sub.3 exhibits strong red
emission (.lamda..sub.max .about.690 nm) in such solutions. The
Au.sub.3Pz.sub.3 emission is found to be sensitive to sub-ppm/nM
levels of silver ions. On addition of silver salt to
Au.sub.3Pz.sub.3/CS aqueous media, a bright-green emissive adduct
(Au.sub.3Pz.sub.3/Ag.sup.+) with peak maximum within 475-515 nm is
developed. The silver adduct in solution exhibits a four-fold
increase in quantum yield (0.19.+-.0.02) compared to
Au.sub.3Pz.sub.3 alone (0.05.+-.0.01), along with a corresponding
increase in phosphorescence lifetime. With almost zero interference
from 15 other metal ions tested, Au.sub.3Pz.sub.3 exhibits extreme
selectivity for Ag.sup.+ with a 0.02 ppm detection limit.
Au.sub.3Pz.sub.3 exhibits sensitivity to higher concentrations
(>1 mM) of other metal ions (Tl.sup.+/Pb.sup.2+/Gd.sup.3+). The
sensing methodology is simple, fast, convenient, and can even be
detected by the naked eye. On addition of
ethylenediaminetetraacetic acid (EDTA), the red emission of
Au.sub.3Pz.sub.3 is restored. Au.sub.3Pz.sub.3 and its silver
adduct retain their characteristic photophysical properties in
thin-film forms. Remarkable photostability with <7%
photobleaching after 4 hours of UV irradiation is attained for
Au.sub.3Pz.sub.3 solutions or thin films.
[0008] Accordingly, this disclosure provides a trinuclear Au(I)
complex of Formula I:
##STR00001##
or an ion thereof, wherein: [0009] R.sup.1 is --CO.sub.2H, or
branched or unbranched --(C.sub.1-C.sub.6)alkyl-CO.sub.2H; and
[0010] R.sup.2 is H, halo, branched or unbranched
--(C.sub.1-C.sub.6)alkyl, or aryl; wherein --(C.sub.1-C.sub.6)alkyl
and aryl are optionally substituted. The pyrazole heterocycle can
also be replaced with other nitrogen heterocycles having a
carboxylic acid substituent, for example, a pyridazine or other
nitrogen heterocycle comprising two nitrogen atoms in the ring.
[0011] This disclosure also provides a chemosensor composition
comprising: [0012] a) a cyclic gold (I) trimer; [0013] b) a
nitrogen heterocycle having a carboxylic acid substituent; and
[0014] c) a polysaccharide in aqueous media at a pH of about the
pKa of the polysaccharide;
[0015] wherein the gold (I) trimer and the heterocycle form a
complex, or an ion thereof, via N--Au--N bonds, and the composition
is phosphorescent, exhibits a red emission, and has a Stokes shift
of about 150 nm or greater.
[0016] Additionally, this disclosure provides a method of
chemosensing metal ions comprising: [0017] a) contacting a sample
comprising metal ions with the chemosensor composition according to
the disclosure above, wherein the chemosensor composition forms
phosphorescent adducts with the metal ions; and [0018] b) sensing
the emission color of the phosphorescent adducts;
[0019] wherein the metal ions are sensed via a difference in the
emission color of the chemosensor composition described above and
the phosphorescent adducts.
[0020] Furthermore, this disclosure provides a method of sensing a
presence or absence of silver ions in a sample comprising: [0021]
a) contacting a sample with the chemosensor composition according
to the disclosure above to form a mixture, wherein the chemosensor
composition forms a phosphorescent adduct with a silver ion when
the sample comprises silver ions; and [0022] b) sensing the
emission color of the mixture;
[0023] wherein a presence of silver ions in the sample is sensed
via a difference in the emission color of the chemosensor
composition and the mixture when the concentration of silver ions
in the sample is above about 5 ppb; and
[0024] wherein an absence of presence of silver ions in the sample
is sensed via no essential difference in the emission color of the
chemosensor composition and the mixture when the concentration of
silver ions in the sample is below about 5 ppb.
[0025] The invention provides a novel complex of Formula I,
intermediates for the synthesis of a complex of Formula I, as well
as methods of preparing a complex of Formula I. The invention also
provides a complex Formula I that are useful as intermediates for
the synthesis of other useful complexes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The following drawings form part of the specification and
are included to further demonstrate certain embodiments or various
aspects of the invention. In some instances, embodiments of the
invention can be best understood by referring to the accompanying
drawings in combination with the detailed description presented
herein. The description and accompanying drawings may highlight a
certain specific example, or a certain aspect of the invention.
However, one skilled in the art will understand that portions of
the example or aspect may be used in combination with other
examples or aspects of the invention.
[0027] FIG. 1. PL spectra of Au.sub.3Pz.sub.3 in CS polymer vs
polymer-free aqueous media at pH .about.6.5 and RT. The inset shows
pictures of red-emissive Au.sub.3Pz.sub.3 synthesized in CS polymer
(top photo) and polymer-free media (bottom photo). Quantum yield
and lifetime values are labeled. Solid and dashed lines represent
Au.sub.3Pz.sub.3 in aqueous CS media and polymer-free DI water,
respectively. The solid line indicating a weak emission from a
CS/pyrazole control solution is also shown.
[0028] FIG. 2. Typical photoluminescence spectra of
Au.sub.3Pz.sub.3 (dark lines) and Au.sub.3Pz.sub.3/Ag.sup.+ (grey
lines) in aqueous CS media at pH .about.6.5 and RT. The solid lines
represent emission spectra and dashed lines represent excitation
spectra. The inset shows quantum yield and lifetime values for
complex and adduct.
[0029] FIG. 3. Selectivity of Au.sub.3Pz.sub.3 to silver over
various other metals in aqueous CS media at pH .about.6.5 and RT.
Titration with 4.97 .mu.M concentration of each salt. (A) Emission
spectra at 325 nm excitation after addition of each metal ion
individually, (B) Folds of enhancement of emission intensity at
.about.475 nm. I.sub.o and I refer the emission intensity before
and after addition of metal ions. (a=Pb.sup.2+, b=Li.sup.+,
c=Zn.sup.2+, d=Co.sup.2+, e=Cd.sup.2+, f=Fe.sup.3+, g=Hg.sup.2+,
h=Cu.sup.2-, i=Ni.sup.2+, j=Al.sup.3+, k=Cs.sup.+, l=K.sup.+,
m=Tl.sup.+, n=Eu.sup.3+, o=Gd.sup.3+). The "*" indicates weak
emission from impurities in chitosan. Pictures were taken with a
handheld UV lamp.
[0030] FIG. 4. Measurement range and detection limits of silver
sensor. A) Titration of Au.sub.3Pz.sub.3 in 1.0 w/w % CS with
gradual addition of Ag.sup.+ aliquots (0.fwdarw.11 ppm in 0.52 ppm
increments) at pH .about.6.5 (.lamda..sub.exc 325 nm/.lamda..sub.em
475 nm; inset shows the schematic illustration of Auz.sub.3Pz.sub.3
interactions with Ag.sup.+). B) I/I.sub.o for detection limit based
on 10% intensity change; the B' inset zooms out the 0.fwdarw.2.1
ppm region with 0.005 ppm increments.
[0031] FIG. 5. Photoluminescence spectra demonstrating
reversibility of silver sensing using EDTA. (Black
solid--Au.sub.3Pz.sub.3; Grey solid/Grey
dashed--Au.sub.3Pz.sub.3/Ag.sup.+; Black dash/Black dotted
(overlapped with black solid)--Au.sub.3Pz.sub.3/Ag.sup.+/EDTA).
[0032] FIG. 6. PL spectra of different heavy-metal ions in aqueous
Au.sub.3Pz.sub.3/CS at pH .about.6.5 and RT. Color coding (arrows):
Blue=Tl.sup.+ (85 mM); Dark cyan=Gd.sup.3+ (0.7 mM); Cyan=Pb.sup.2+
(100 mM); Green=Ag.sup.+; Red=Gd.sup.3+ * (0.7 mM);
White=Ag.sup.+/Tl.sup.- (1:1:1 volume admixture with
Au.sub.3Pz.sub.3). Inset shows pictures of different adducts under
handheld UV lamp (365 nm except Gd.sup.3+ * used 254 nm). Refer to
FIG. 13 and FIG. 14 for excitation spectra.
[0033] FIG. 7. Photophysical properties of thin films of
Au.sub.3Pz.sub.3 and Au.sub.3Pz.sub.3/Ag.sup.+ adduct in CS. The
dark and grey solid lines represent the emission spectra of
Au.sub.3Pz.sub.3 and the silver adduct, respectively. The dashed
dark and grey lines represent the excitation spectra of
Au.sub.3Pz.sub.3 and Au.sub.3Pz.sub.3/Ag.sup.+, respectively. The
black solid and dashed lines (below about 300 nm) represent the
UV/vis absorption spectra of Au.sub.3Pz.sub.3 and the silver
adduct, respectively. Insets show emissive films under hand-held UV
lamp at 254 nm for Au.sub.3Pz.sub.3 and at 365 nm for
Au.sub.3Pz.sub.3/Ag.sup.+ adduct. Lifetime values and quantum yield
numbers are also listed.
[0034] FIG. 8. Photostability experiment of Au.sub.3Pz.sub.3 in
aqueous solution of chitosan polymer at room temperature.
Illumination was performed under 290 nm UV excitation for 4 hours.
The overlapping PL data are monitored before (grey-colored spectra)
and after illuminating for 4 hr (dark-colored spectra); emission
spectra are on the right side while luminescence excitation spectra
are on the left side. A total 6.9% photo-degradation in 4 hours is
obtained from the results shown in the inset, which represent an
upper limit given the experiments did not account for lamp
intensity drift.
[0035] FIG. 9. The interference effect of Au.sub.3Pz.sub.3 for
silver sensitivity. (A) Titration data. (B) I/I.sub.0 data.
[0036] FIG. 10. (A) Photoluminescence spectra of Au.sub.3Pz.sub.3
in 1.0 w/v % CS solution (.lamda..sub.exc 305 nm and
.lamda..sub.emi 475 nm, pH .about.6.5 at room temperature) upon
gradual addition of silver ion from 0 to 0.05 ppm for determining
the detection limit based on 10% change in emission intensity. (B)
Linearity between emission ratio vs silver concentration (from 0 to
2.1 ppm) for the same purpose of determining the detection
limit.
[0037] FIG. 11. (A) PL spectral titration of Au.sub.3Pz.sub.3 in
1.0% CS upon addition of a 0.52-ppm aliquot of Ag.sup.- using
.lamda..sub.exc=325 nm at pH 6.5, showing the full (top) and zoomed
(bottom) range. (B) PL spectral titration of Au.sub.3Pz.sub.3 in
1.0% CS upon addition of 0.53-ppm and 1.06-ppm consecutive aliquots
of Ag.sup.+ using .lamda..sub.exc=325 nm at pH 6.5, showing the
baseline-corrected spectra (top) and data manipulation thereof
(bottom) range.
[0038] FIG. 12. (A) PL spectral titration of Au.sub.3Pz.sub.3 in
0.1% CS/0-2.2 ppm upon addition of a 0.05341-ppm aliquot of
Ag.sup.+ (.lamda..sub.exc=325 nm; pH 6.5). (B) PL spectral
titration of Au.sub.3Pz.sub.3 in 0.1% CS/0-2.2 ppm upon addition of
0.11-ppm and 0.27-ppm consecutive aliquots of Ag.sup.+ using
.lamda..sub.exc=325 nm at pH 6.5, showing the baseline-corrected
spectra (top) and data manipulation thereof (bottom) range.
[0039] FIG. 13. (A) PL spectral titration of Au.sub.3Pz.sub.3 in
0.1% CS/0-11 ppm upon addition of a 0.53-ppm aliquot of Ag.sup.+
(.lamda..sub.exc=325 nm; pH 6.5), showing the full (top) and zoomed
(bottom) range. (B) PL spectral titration of Au.sub.3Pz.sub.3 in
0.1% CS/0-11 ppm upon addition of 0.53-ppm and 2.10-ppm consecutive
aliquots of Ag.sup.+ using .lamda..sub.exc=325 nm at pH 6.5,
showing the baseline-corrected spectra (top) and data manipulation
thereof (bottom) range.
[0040] FIG. 14. (A) PL spectra of titration of Au.sub.3Pz.sub.3 in
aqueous solution of chitosan upon of gradual addition
[(0.fwdarw.103 .mu.M; increments of 4.97 .mu.M); 0, 4.97, 9.90,
14.77, 19.60, 24.39, 29.12, 33.81, 38.46, 43.06, 47.61, 52.13,
56.60, 61.03, 65.42, 69.76, 74.07, 78.34, 82.56, 86.75, 90.09,
95.02, 99.09, 103.13 .mu.M)] of Ag.sup.- at excitation 285 nm at pH
6.5 (.about.470 nm). (B) Plot of emission of integrated total peak
area of Au.sub.3Pz.sub.3 as a function of concentration of Ag.sup.+
ion. I.sub.0 and I is before and after addition of Ag.sup.+ ion,
respectively.
[0041] FIG. 15. Job plots: The stoichiometry of
Ag.sup.+/Au.sub.3Pz.sub.3 adduct was determined by continuous
variation method or Job plot. The solutions of AgNO.sub.3 and
Au.sub.3Pz.sub.3 of equal concentrations were prepared in DI water
and in chitosan solution, respectively. Next, solutions of Ag.sup.+
and Au.sub.3Pz.sub.3 were mixed at different proportions by
maintaining a total volume of 3 mL for the mixture. The different
ratios of Au.sub.3Pz.sub.3:Ag.sup.+ (v/v) were 3.000:0,
2.990:0.010, 2.980:0.020, 2.970:0.030, 2.960:0.040, 2.950:0.050,
2.940:0.060, 2.930:0.070, 2.920:0.080, 2.910:0.090, 2.900:0.100,
2.800:0.200, 2.6:0.4, 2.4:0.6, 2.2:0.8, 2:1, 1.8:1.2, 1.6:1.4,
1.5:1.5, 1.4:1.6, 1.2:1.8, 1:2, 0.8:2.2, 0.6:2.4, 0.4:2.6, 0.2:2.8,
and 0:3. The emission spectra were recorded immediately after
preparing these samples. The emission intensity at 525 nm was used
to plot the graph against mole fractions of
[Ag.sup.+]/([Ag.sup.+]+[Au.sub.3Pz.sub.3]). In the plot, the mole
fraction of Ag.sup.+ at which the summed concentration of
([Ag.sup.+]+[Au.sub.3Pz.sub.3]) gives maximum emission intensity
indicates the stoichiometry of Ag.sup.+:Au.sub.3Pz.sub.3.
[0042] FIG. 16. Excitation for different metal adducts.
[0043] FIG. 17. Comparing the emission spectra of different metal
adducts vs a control chitosan/pyrazole (CS-Pz) aqueous solution
indicated as a dotted line, demonstrating lack of signal
interference for each composition from that of any other.
[0044] FIG. 18. (A) PL data of red thin-film of Au.sub.3Pz.sub.3
obtained from chitosan-stabilized solution. Insect a picture of red
film at room temperature with UV handheld lamp (short wavelength
254 nm). (B) Measurements of absolute quantum yields of red
thin-film (of A). The average measured absolute quantum yield is
48.5%.
[0045] FIG. 19. A) Spectra of AuT alone, AuT+Ag, AuT+AgNP, and 1 wt
% CS. Inset photographs were taken under a hand-held UV lamp under
both long and short wavelength (254 nm and 365 nm) associated with
the spectra. B) Square dotted line: One addition of AgNP with
subsequent additions of Ag.sup.+ ions. Round dotted line: One
addition of silver ions with subsequent additions of AgNPs. The
Ag.sup.+ ions were prepared at the same concentration as the AgNPs.
For all PL, spectra .lamda..sub.ex=320 nm and .lamda..sub.em=475
nm.
[0046] FIG. 20. A) AuT sensing the leaching of silver ions from
20-nM AgNPs over 35 days. The control spectrum of the silver ion
titration was done at the same concentration as the AgNP (0.02
mg/mL). B) UV-Vis spectra of 20-nM AgNPs. Spectra were collected
the same day the data in A were taken. Inset chart shows the change
in FWHM and peak maximum of the AgNP UV-Vis spectra over 35 days.
All PL spectra were collected with .lamda..sub.ex=320 nm and
.lamda..sub.em=475 nm.
[0047] FIG. 21. A) AuT sensing of silver ion concentration of
100-nM AgNPs before and after the AgNPs have been dialyzed for 7
days. B) UV-Vis spectra of the 100-nM AgNPs before and after
dialysis. Spectra were collected the same day the data in A were
taken. For all PL spectra, .lamda..sub.ex=320 nm and
.lamda..sub.em=475 nm.
[0048] FIG. 22. A) AuT silver sensitivity at pH 4 and pH 6 in
water. Inset graphic shows the change of the carboxylic acid
functional group to carboxylate at pH 4 and pH 6. B) AuT
remediation of silver ions in water at pH 6. Silver ions were added
to a solution of AuT then excess KCl was added. A fresh solution of
AuT was used for every point from the same stock solution. C) AuT
remediation of silver ions in water at pH 6. KCl was first added to
the AuT then a silver titration was performed. This data set was
compared to the control data set (square dotted line)--which was a
silver titration with AuT where no KCl was present. For all PL
spectra, .lamda..sub.ex=320 nm and .lamda..sub.em=475 nm.
[0049] FIG. 23. PL spectra of Au.sub.3Pz.sub.3 in different media
at RT. The inset shows pictures of red-emissive Au.sub.3Pz.sub.3
synthesized in different media. The Au.sub.3Pz.sub.3 is synthesized
and stabilized in PAA (polyacrylic acid media) at two different pH
(pH 7.0 and 9.0); CS-Oligo (chitosan oligosaccharide lactate); RPMI
(Roswell Park Memorial Institute) 1640 and phosphate buffer media.
The emission and excitation spectra are shown in the figure.
DETAILED DESCRIPTION
[0050] Herein is described the investigation of heavy metal sensing
that relies on the formation of sandwich Au(I) trimer adducts in
aqueous media, resulting in distinguishable luminescent properties.
A majority of the Au(I) trimer complexes exhibit intertrimer
association in the solid state with very few known examples in
solution (mostly organic solvents). In the solid state, intertrimer
and intratrimer aurophilic interactions usually manifest themselves
by ca. 3.0-3.7 .ANG. crystallographic Au . . . Au distances, which
significantly shorten when the molecule is excited to form excited
state oligomers (excimers/extended excimers) with bona fide Au . .
. Au covalent bonds. Monomeric units of Au(I) trimer complexes can
exist in infinitesimally dilute solutions that preclude intertrimer
aurophilic interactions. Consequently, in most cases, this renders
many Au(I) trimer complexes non-luminescent in dilute solutions. At
higher concentrations and in organogels these trimer complexes can
exhibit detectable luminescence. In the present case, to help
stabilize the Au . . . Au interactions in aqueous media, a natural
linear polysaccharide polymer, chitosan (CS), is employed. CS is
known specifically for its biocompatible, biodegradable, and
nontoxic properties.
[0051] Silver nanoparticles (AgNPs) have well-known antibacterial
properties that have stimulated their widespread production and
usage, which nonetheless concomitantly raises concerns regarding
their release into the environment. Understanding the toxicity of
AgNPs to biological systems, the environment, and the role that
each silver species (Ag.sup.+ ions vs AgNPs) plays in that toxicity
has received significant attention. One of the critical objectives
of this research is the development of a reliable method that can
sense and differentiate free silver ions from AgNPs and is able to
characterize silver ions leaching from the nanosilver. Several
analytical methods described in the literature that are available
for sensing silver ions are costly, time-consuming, tedious, and
more importantly, destroy the AgNP sample. To address these issues,
a phosphorescent gold(I)-pyrazolate cyclic trinuclear complex (AuT)
known to detect free silver ions was employed to detect and
differentiate silver ions from AgNPs within an AgNP sample.
[0052] The advantage of the silver sensor is its ratiometric
emission capability that undermines any background interference.
The sensor exhibits a strong red emission (.lamda..sub.max
.about.690 nm) that--in the presence of Ag.sup.+ ions will form a
bright-green emissive adduct with a peak maximum near 475 nm. The
presence of AgNPs did not inhibit the silver detection and
quantification ability of the phosphorescent silver sensor. In
order to understand the chemical transformation of nanosilver, the
leaching of silver ions from AgNPs over a period of 35 days was
monitored and quantified by measuring the I/I.sub.0 changes of the
sensor. Furthermore, through adduct formation, the AuT molecular
system was able to remediate free silver ions from the solution.
The stronger affinity of the AuT complex to "sandwich" free silver
ions was demonstrated in the presence of a KCl salt that is
well-documented to form AgCl in the presence of silver ions. This
is the only ratiometric luminescence-based silver sensor able to
successfully differentiate between Ag.sup.+ ions and AgNPs, sense
the silver leakage from AgNPs, and remediate toxic silver ions from
solution.
Definitions
[0053] The following definitions are included to provide a clear
and consistent understanding of the specification and claims. As
used herein, the recited terms have the following meanings. All
other terms and phrases used in this specification have their
ordinary meanings as one of skill in the art would understand. Such
ordinary meanings may be obtained by reference to technical
dictionaries, such as Hawley's Condensed Chemical Dictionary
14.sup.th Edition, by R. J. Lewis, John Wiley & Sons, New York,
N.Y., 2001.
[0054] References in the specification to "one embodiment", "an
embodiment", etc., indicate that the embodiment described may
include a particular aspect, feature, structure, moiety, or
characteristic, but not every embodiment necessarily includes that
aspect, feature, structure, moiety, or characteristic. Moreover,
such phrases may, but do not necessarily, refer to the same
embodiment referred to in other portions of the specification.
Further, when a particular aspect, feature, structure, moiety, or
characteristic is described in connection with an embodiment, it is
within the knowledge of one skilled in the art to affect or connect
such aspect, feature, structure, moiety, or characteristic with
other embodiments, whether or not explicitly described.
[0055] The singular forms "a," "an," and "the" include plural
reference unless the context clearly dictates otherwise. Thus, for
example, a reference to "a compound" includes a plurality of such
compounds, so that a compound X includes a plurality of compounds
X. It is further noted that the claims may be drafted to exclude
any optional element. As such, this statement is intended to serve
as antecedent basis for the use of exclusive terminology, such as
"solely," "only," and the like, in connection with any element
described herein, and/or the recitation of claim elements or use of
"negative" limitations.
[0056] The term "and/or" means any one of the items, any
combination of the items, or all of the items with which this term
is associated. The phrases "one or more" and "at least one" are
readily understood by one of skill in the art, particularly when
read in context of its usage. For example, the phrase can mean one,
two, three, four, five, six, ten, 100, or any upper limit
approximately 10, 100, or 1000 times higher than a recited lower
limit.
[0057] As will be understood by the skilled artisan, all numbers,
including those expressing quantities of ingredients, properties
such as molecular weight, reaction conditions, and so forth, are
approximations and are understood as being optionally modified in
all instances by the term "about." These values can vary depending
upon the desired properties sought to be obtained by those skilled
in the art utilizing the teachings of the descriptions herein. It
is also understood that such values inherently contain variability
necessarily resulting from the standard deviations found in their
respective testing measurements. When values are expressed as
approximations, by use of the antecedent "about," it will be
understood that the particular value without the modifier "about"
also forms a further aspect.
[0058] The terms "about" and "approximately" are used
interchangeably. Both terms can refer to a variation of .+-.5%,
.+-.10%, .+-.20%, or .+-.25% of the value specified. For example,
"about 50" percent can in some embodiments carry a variation from
45 to 55 percent, or as otherwise defined by a particular claim.
For integer ranges, the term "about" can include one or two
integers greater than and/or less than a recited integer at each
end of the range. Unless indicated otherwise herein, the terms
"about" and "approximately" are intended to include values, e.g.,
weight percentages, proximate to the recited range that are
equivalent in terms of the functionality of the individual
ingredient, composition, or embodiment. The terms "about" and
"approximately" can also modify the endpoints of a recited range as
discussed above in this paragraph.
[0059] As will be understood by one skilled in the art, for any and
all purposes, particularly in terms of providing a written
description, all ranges recited herein also encompass any and all
possible sub-ranges and combinations of sub-ranges thereof, as well
as the individual values making up the range, particularly integer
values. It is therefore understood that each unit between two
particular units are also disclosed. For example, if 10 to 15 is
disclosed, then 11, 12, 13, and 14 are also disclosed,
individually, and as part of a range. A recited range (e.g., weight
percentages or carbon groups) includes each specific value,
integer, decimal, or identity within the range. Any listed range
can be easily recognized as sufficiently describing and enabling
the same range being broken down into at least equal halves,
thirds, quarters, fifths, or tenths. As a non-limiting example,
each range discussed herein can be readily broken down into a lower
third, middle third and upper third, etc. As will also be
understood by one skilled in the art, all language such as "up to",
"at least", "greater than", "less than", "more than", "or more",
and the like, include the number recited and such terms refer to
ranges that can be subsequently broken down into sub-ranges as
discussed above. In the same manner, all ratios recited herein also
include all sub-ratios falling within the broader ratio.
Accordingly, specific values recited for radicals, substituents,
and ranges, are for illustration only; they do not exclude other
defined values or other values within defined ranges for radicals
and substituents. It will be further understood that the endpoints
of each of the ranges are significant both in relation to the other
endpoint, and independently of the other endpoint.
[0060] One skilled in the art will also readily recognize that
where members are grouped together in a common manner, such as in a
Markush group, the invention encompasses not only the entire group
listed as a whole, but each member of the group individually and
all possible subgroups of the main group. Additionally, for all
purposes, the invention encompasses not only the main group, but
also the main group absent one or more of the group members. The
invention therefore envisages the explicit exclusion of any one or
more of members of a recited group. Accordingly, provisos may apply
to any of the disclosed categories or embodiments whereby any one
or more of the recited elements, species, or embodiments, may be
excluded from such categories or embodiments, for example, for use
in an explicit negative limitation.
[0061] The term "contacting" refers to the act of touching, making
contact, or of bringing to immediate or close proximity, including
at the cellular or molecular level, for example, to bring about a
physiological reaction, a chemical reaction, or a physical change,
e.g., in a solution, in a reaction mixture, in vitro, or in
vivo.
[0062] The term "substantially" as used herein, is a broad term and
is used in its ordinary sense, including, without limitation, being
largely but not necessarily wholly that which is specified. For
example, the term could refer to a numerical value that may not be
100% the full numerical value. The full numerical value may be less
by about1%, about 2%, about 3%, about 4%, about 5%, about 6%, about
7%, about 8%, about 9%, about 10%, about 15%, or about 20%.
[0063] This disclosure provides methods of making the compounds and
compositions of the invention. The compounds and compositions can
be prepared by any of the applicable techniques described herein,
optionally in combination with standard techniques of organic
synthesis. Many techniques such as etherification and
esterification are well known in the art. However, many of these
techniques are elaborated in Compendium of Organic Synthetic
Methods (John Wiley & Sons, New York), Vol. 1, Ian T. Harrison
and Shuyen Harrison, 1971; Vol. 2, Ian T. Harrison and Shuyen
Harrison, 1974; Vol. 3, Louis S. Hegedus and Leroy Wade, 1977; Vol.
4, Leroy G. Wade, Jr., 1980; Vol. 5, Leroy G. Wade, Jr., 1984; and
Vol. 6; as well as standard organic reference texts such as March's
Advanced Organic Chemistry: Reactions, Mechanisms, and Structure,
5th Ed., by M. B. Smith and J. March (John Wiley & Sons, New
York, 2001); Comprehensive Organic Synthesis. Selectivity, Strategy
& Efficiency in Modern Organic Chemistry. In 9 Volumes, Barry
M. Trost, Editor-in-Chief (Pergamon Press, New York, 1993
printing); Advanced Organic Chemistry, Part B: Reactions and
Synthesis, Second Edition, Cary and Sundberg (1983).
[0064] The formulas and compounds described herein can be modified
using protecting groups. Suitable amino and carboxy protecting
groups are known to those skilled in the art (see for example,
Protecting Groups in Organic Synthesis, Second Edition, Greene, T.
W., and Wutz, P. G. M., John Wiley & Sons, New York, and
references cited therein; Philip J. Kocienski; Protecting Groups
(Georg Thieme Verlag Stuttgart, New York, 1994), and references
cited therein); and Comprehensive Organic Transformations, Larock,
R. C., Second Edition, John Wiley & Sons, New York (1999), and
referenced cited therein.
[0065] As used herein, the term "substituted" or "substituent" is
intended to indicate that one or more (for example., 1-20 in
various embodiments, 1-10 in other embodiments, 1, 2, 3, 4, or 5;
in some embodiments 1, 2, or 3; and in other embodiments 1 or 2)
hydrogens on the group indicated in the expression using
"substituted" (or "substituent") is replaced with a selection from
the indicated group(s), or with a suitable group known to those of
skill in the art, provided that the indicated atom's normal valency
is not exceeded, and that the substitution results in a stable
compound. Suitable indicated groups include, e.g., alkyl, alkenyl,
alkynyl, alkoxy, halo, haloalkyl, hydroxy, hydroxyalkyl, aryl,
heteroaryl, heterocycle, cycloalkyl, alkanoyl, alkoxycarbonyl,
amino, alkylamino, dialkylamino, trifluoromethylthio,
difluoromethyl, acylamino, nitro, trifluoromethyl,
trifluoromethoxy, carboxy, carboxyalkyl, keto, thioxo, alkylthio,
alkylsulfinyl, alkylsulfonyl, and cyano. Additionally, non-limiting
examples of substituents that can be bonded to a substituted carbon
(or other) atom include F, Cl, Br, I, OR', OC(O)N(R').sub.2, CN,
CF.sub.3, OCF.sub.3, R', O, S, C(O), S(O), methylenedioxy,
ethylenedioxy, N(R').sub.2, SR', SOR', SO.sub.2R',
SO.sub.2N(R').sub.2, SO.sub.3R', C(O)R', C(O)C(O)R',
C(O)CH.sub.2C(O)R', C(S)R', C(O)OR', OC(O)R', C(O)N(R').sub.2,
OC(O)N(R').sub.2, C(S)N(R').sub.2, (CH.sub.2).sub.0-2NHC(O)R',
N(R')N(R')C(O)R', N(R')N(R')C(O)OR', N(R')N(R')CON(R').sub.2,
N(R')SO.sub.2R', N(R')SO.sub.2N(R').sub.2, N(R')C(O)OR',
N(R')C(O)R', N(R')C(S)R', N(R')C(O)N(R').sub.2,
N(R')C(S)N(R').sub.2, N(COR')COR', N(OR')R', C(.dbd.NH)N(R').sub.2,
C(O)N(OR')R', or C(.dbd.NOR')R' wherein R' can be hydrogen or a
carbon-based moiety, and wherein the carbon-based moiety can itself
be further substituted. When a substituent is monovalent, such as,
for example, F or Cl, it is bonded to the atom it is substituting
by a single bond. When a substituent is more than monovalent, such
as O, which is divalent, it can be bonded to the atom it is
substituting by more than one bond, i.e., a divalent substituent is
bonded by a double bond; for example, a C substituted with O forms
a carbonyl group, C.dbd.O, wherein the C and the O are double
bonded. Alternatively, a divalent substituent such as O, S, C(O),
S(O), or S(O).sub.2 can be connected by two single bonds to two
different carbon atoms. For example, O, a divalent substituent, can
be bonded to each of two adjacent carbon atoms to provide an
epoxide group, or the O can form a bridging ether group between
adjacent or non-adjacent carbon atoms, for example bridging the
1,4-carbons of a cyclohexyl group to form a [2.2.1]-oxabicyclo
system. Further, any substituent can be bonded to a carbon or other
atom by a linker, such as (CH.sub.2).sub.n or (CR'.sub.2).sub.n
wherein n is 1, 2, 3, or more, and each R' is independently
selected.
[0066] The term "halo" or "halide" refers to fluoro, chloro, bromo,
or iodo. Similarly, the term "halogen" refers to fluorine,
chlorine, bromine, and iodine.
[0067] The term "alkyl" refers to a branched or unbranched
hydrocarbon having, for example, from 1-20 carbon atoms, and often
1-12, 1-10, 1-8, 1-6, or 1-4 carbon atoms. As used herein, the term
"alkyl" also encompasses a "cycloalkyl", defined below. Examples
include, but are not limited to, methyl, ethyl, 1-propyl, 2-propyl
(iso-propyl), 1-butyl, 2-methyl-1-propyl (isobutyl), 2-butyl
(sec-butyl), 2-methyl-2-propyl (t-butyl), 1-pentyl, 2-pentyl,
3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl,
2-methyl-1-butyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl,
3-methyl-2-pentyl, 4-methyl-2-pentyl, 3-methyl-3-pentyl,
2-methyl-3-pentyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl,
hexyl, octyl, decyl, dodecyl, and the like. The alkyl can be
unsubstituted or substituted, for example, with a substituent
described below. The alkyl can also be optionally partially or
fully unsaturated. As such, the recitation of an alkyl group can
include both alkenyl and alkynyl groups. The alkyl can be a
monovalent hydrocarbon radical, as described and exemplified above,
or it can be a divalent hydrocarbon radical (i.e., an
alkylene).
[0068] The term "cycloalkyl" refers to cyclic alkyl groups of, for
example, from 3 to 10 carbon atoms having a single cyclic ring or
multiple condensed rings. Cycloalkyl groups include, by way of
example, single ring structures such as cyclopropyl, cyclobutyl,
cyclopentyl, cyclooctyl, and the like, or multiple ring structures
such as adamantyl, and the like. The cycloalkyl can be
unsubstituted or substituted. The cycloalkyl group can be
monovalent or divalent and can be optionally substituted as
described for alkyl groups. The cycloalkyl group can optionally
include one or more cites of unsaturation, for example, the
cycloalkyl group can include one or more carbon-carbon double
bonds, such as, for example, 1-cyclopent-1-enyl,
1-cyclopent-2-enyl, 1-cyclopent-3-enyl, cyclohexyl,
1-cyclohex-1-enyl, 1-cyclohex-2-enyl, 1-cyclohex-3-enyl, and the
like.
[0069] The term "aryl" refers to an aromatic hydrocarbon group
derived from the removal of at least one hydrogen atom from a
single carbon atom of a parent aromatic ring system. The radical
attachment site can be at a saturated or unsaturated carbon atom of
the parent ring system. The aryl group can have from 6 to 30 carbon
atoms, for example, about 6-10 carbon atoms. In other embodiments,
the aryl group can have 6 to 60 carbons atoms, 6 to 120 carbon
atoms, or 6 to 240 carbon atoms. The aryl group can have a single
ring (e.g., phenyl) or multiple condensed (fused) rings, wherein at
least one ring is aromatic (e.g., naphthyl, dihydrophenanthrenyl,
fluorenyl, or anthryl). Typical aryl groups include, but are not
limited to, radicals derived from benzene, naphthalene, anthracene,
biphenyl, and the like. The aryl can be unsubstituted or optionally
substituted.
[0070] The term "heteroaryl" refers to a monocyclic, bicyclic, or
tricyclic ring system containing one, two, or three aromatic rings
and containing at least one nitrogen, oxygen, or sulfur atom in an
aromatic ring. The heteroaryl can be unsubstituted or substituted,
for example, with one or more, and in particular one to three,
substituents, as described in the definition of "substituted".
Typical heteroaryl groups contain 2-20 carbon atoms in the ring
skeleton in addition to the one or more heteroatoms. Examples of
heteroaryl groups include, but are not limited to, 2H-pyrrolyl,
3H-indolyl, 4H-quinolizinyl, acridinyl, benzo[b]thienyl,
benzothiazolyl, .beta.-carbolinyl, carbazolyl, chromenyl,
cinnolinyl, dibenzo[b,d]furanyl, furazanyl, furyl, imidazolyl,
imidizolyl, indazolyl, indolisinyl, indolyl, isobenzofuranyl,
isoindolyl, isoquinolyl, isothiazolyl, isoxazolyl, naphthyridinyl,
oxazolyl, perimidinyl, phenanthridinyl, phenanthrolinyl,
phenarsazinyl, phenazinyl, phenothiazinyl, phenoxathiinyl,
phenoxazinyl, phthalazinyl, pteridinyl, purinyl, pyranyl,
pyrazinyl, pyrazolyl, pyridazinyl, pyridyl, pyrimidinyl, pyrrolyl,
quinazolinyl, quinolyl, quinoxalinyl, thiadiazolyl, thianthrenyl,
thiazolyl, thienyl, triazolyl, tetrazolyl, and xanthenyl. In one
embodiment the term "heteroaryl" denotes a monocyclic aromatic ring
containing five or six ring atoms containing carbon and 1, 2, 3, or
4 heteroatoms independently selected from non-peroxide oxygen,
sulfur, and N(Z) wherein Z is absent or is H, O, alkyl, aryl, or
(C.sub.1-C.sub.6)alkylaryl. In some embodiments, heteroaryl denotes
an ortho-fused bicyclic heterocycle of about eight to ten ring
atoms derived therefrom, particularly a benz-derivative or one
derived by fusing a propylene, trimethylene, or tetramethylene
diradical thereto.
[0071] The term "complex" or "coordination complex" refers to a
central atom or ion, which is metallic and is called the
coordination center, and a surrounding array of bound molecules or
ions, that are in turn known as ligands or complexing agents. Many
metal-containing compounds, especially those of transition metals,
for example, silver and gold, are coordination complexes.
[0072] The term "coordinate covalent bond", refers to a 2-center,
2-electron covalent bond in which the two electrons derive from the
same atom. The bonding of metal ions to ligands involves this kind
of interaction which can be almost as strong as a covalent
bond.
Embodiments of the Invention
[0073] This disclosure provides a trinuclear Au(I) complex of
Formula I:
##STR00002##
or an ion thereof, wherein: [0074] R.sup.1 is --CO.sub.2H, or
branched or unbranched --(C.sub.1-C.sub.6)alkyl-CO.sub.2H; and
[0075] R.sup.2 is H, halo, branched or unbranched
--(C.sub.1-C.sub.6)alkyl, or aryl; wherein --(C.sub.1-C.sub.6)alkyl
and aryl are optionally substituted.
[0076] In some embodiments of the disclosed complex, R.sup.1 is
--CO.sub.2H and R.sup.2 is branched or unbranched
--(C.sub.1-C.sub.6)alkyl. In other embodiments, R.sup.2 is
--CF.sub.3 or --CF.sub.2CF.sub.3.
[0077] This disclosure provides various embodiments of a
chemosensor composition comprising: [0078] a) a cyclic gold(I)
trimer; [0079] b) a nitrogen heterocycle having a carboxylic acid
substituent; [0080] c) a polysaccharide in aqueous media at a pH of
about the pKa of the polysaccharide; [0081] d) an optional acrylic
acid-based polymer media at different pH; and [0082] e) an optional
phosphate buffer media.
[0083] wherein the gold(I) trimer and the heterocycle form a
complex via N--Au--N coordinate covalent bonds, and the composition
is phosphorescent, exhibits a red emission at about the pKa of the
polysaccharide, and has a Stokes shift of at least about 150
nm.
[0084] In some embodiments, the heterocycle is a pyrazole or a
pyridazine, or a heterocycle compatible with the formation of a
cyclic gold(I) trimer. In other embodiments, the polysaccharide is
a glycosaminoglycan or chitosan. In yet other embodiments, the
amount of the polysaccharide in aqueous media is about 0.05% wt/v
to about 5% wt/v, or about 0.1% wt/v to about 2% wt/v. In further
embodiments, the molecular weight of the polysaccharide,
glycosaminoglycan or chitosan is about 1 kDa to about 1000 kDa,
about 50 kDa to about 800 kDa, about 100 kDa to about 600 kDa,
about 200 kDa to about 500 kDa, or about 150 kDa to about 400
kDa.
[0085] In other embodiments, the chemosensor composition comprises
step d) an acrylic acid-based polymer media at different pH. In yet
other embodiments, the chemosensor composition comprises step e) a
phosphate buffer media.
[0086] In further embodiments, the red emission is at a wavelength
of about 650 nm to about 750 nm, or about 700 nm. In additional
embodiments, the pH is about 3.0 to about 8.0, about 6.0 to about
7.5, or about at pH 7. In yet some other embodiments, the Stokes
shift is about 200 nm to about 500 nm. In other embodiments, the
Stokes shift is about 50 nm to about 100 nm, about 100 nm to about
150 nm, about 150 nm to about 200 nm, about 200 nm to about 250 nm,
about 250 nm to about 300 nm, about 300 nm to about 350 nm, about
350 nm to about 400 nm, about 400 nm to about 450 nm, or about 450
nm to about 500 nm.
[0087] In various other embodiments, the chemosensor has a
phosphorescence quantum yield of about 5% or greater and a
phosphorescence lifetime of about 3 microseconds or greater. In
other embodiments, the chemosensor has a phosphorescence quantum
yield of about 1%, about 2%, about 3%, about 4%, about 5%, about
6%, about 7%, about 8%, about 9%, about 10%, or about 10% to about
20%. In further embodiments, the quantum efficiency (.PHI.) is
about 0.01 to about 0.8, about 0.05 to about 0.8, about 0.1 to
about 0.5, or about 0.15 to about 0.3.
[0088] In some other embodiments, the chemosensor has a
phosphorescence lifetime of about 1 microsecond, about 2
microseconds, about 3 microseconds, about 4 microseconds, about 5
microseconds, about 6 microseconds, about 7 microseconds, about 8
microseconds, about 9 microseconds, or about 10 microseconds to
about 25 microseconds.
[0089] In various embodiments of the above disclosed composition,
the complex comprises Formula I:
##STR00003##
or an ion thereof, wherein: [0090] R.sup.1 is --CO.sub.2H, or
branched or unbranched --(C.sub.1-C.sub.6)alkyl-CO.sub.2H; and
[0091] R.sup.2 is H, halo, branched or unbranched
--(C.sub.1-C.sub.6)alkyl, or aryl; wherein --(C.sub.1-C.sub.6)alkyl
and aryl are optionally substituted. In some embodiments, R.sup.2
is --CF.sub.3 or --CF.sub.2CF.sub.3.
[0092] In various embodiments of the above disclosed complex or
chemosensor, each R.sup.1 is independently --CO.sub.2H, or
independently branched or unbranched
--(C.sub.1-C.sub.6)alkyl-CO.sub.2H; and
[0093] each R.sup.2 is independently H, halo, branched or
unbranched --(C.sub.1-C.sub.6)alkyl, or aryl;
[0094] In other embodiments, the complex comprising Formula I is a
complex comprising X:
##STR00004##
or an ion thereof.
[0095] In various embodiments, the complex is stabilized by the
polysaccharide. In additional embodiments, the polysaccharide
comprises amine substituents, and the complex is stabilized via ion
pairing of a carboxylic acid group R.sup.1 of Formula I and an
amino group of the polysaccharide. In further embodiments, the
stabilized complex has a surface charge that is reduced by about 5
mV to about 20 mV relative to a non-stabilized complex of Formula
I. In yet some other embodiments, the composition is photostable
wherein about 4 hours of UV irradiation of the composition results
in less than 10% photobleaching, less than 20% photobleaching, or
less than 5% photobleaching.
[0096] Furthermore, this disclosure provides a composition
comprising the trinuclear Au(I) complex according to the disclosure
above and a metal ion wherein the metal ion is sandwiched by two
complexes to form a sandwich complex. This disclosure also provides
a thin film comprising the chemosensor according to the disclosed
complex or composition, and a substrate.
[0097] Also, the disclosure provides a method of chemosensing metal
ions comprising:
[0098] a) contacting a sample comprising metal ions with the
chemosensor composition according to the disclosure herein, wherein
the chemosensor composition forms phosphorescent adducts with the
metal ions; and
[0099] b) sensing the emission color of the phosphorescent
adducts;
[0100] wherein the metal ions are sensed via a difference in the
emission color of the chemosensor composition disclosed herein and
the phosphorescent adducts.
[0101] In various embodiments, the emission peak of the
phosphorescent adducts is blue shifted. In various other
embodiments, the metal ions are silver, thallium, lead, or
gadolinium. In additional embodiments, the metal ions are silver
ions and the limit of detection of the silver ions being sensed is
about 1 ppb, 5 ppb, about 10 ppb, about 15 ppb, or about 20 ppb to
about 100 ppb. In yet some other embodiments, the emission
intensity of the phosphorescent adducts is at least about 5 times
greater, or about 5 times to about 25 times greater than the
emission intensity of the chemosensor composition disclosed herein.
In further embodiments, addition of a metal chelating agent (such
as but not limited to EDTA) to the phosphorescent adducts restores
the red emission of the chemosensor composition disclosed
herein.
[0102] Additionally, this disclosure provides a method of sensing
(or detecting) a presence or absence of metal ions (e.g. Ag, Pb,
Tl, Gd ions, or mixture of ions thereof) in a sample
comprising:
[0103] a) contacting a sample with the chemosensor composition
according to the disclosure herein to form a mixture, wherein the
chemosensor composition forms a phosphorescent adduct with a metal
(e.g., silver) ion when the sample comprises metal (e.g., silver)
ions; and
[0104] b) sensing the emission color of the mixture;
[0105] wherein a presence of metal (e.g., silver) ions in the
sample is sensed via a difference in the emission color of the
chemosensor composition and the mixture when the concentration of
metal (e.g., silver) ions in the sample is above about 5 ppb;
and
[0106] wherein an absence of metal (e.g., silver) ions in the
sample is sensed via no essential difference in the emission color
of the chemosensor composition and the mixture when the
concentration of metal (e.g., silver) ions in the sample is about
0.1 ppm to about 20 ppm (or below about 5 ppb for silver ions).
[0107] In various other embodiments, a green emissive adduct
indicates a concentration of silver ions of at least 5 ppb. In
other embodiments, the sample comprises silver nanoparticles. In
some other embodiments, the chemosensor composition is insensitive
to zero-valent silver (Ag.sup.0). In further embodiments, sensing
the emission color of the mixture is unchanged or substantially
unchanged when the presence of salts (for example, potassium
chloride) is in the sample.
[0108] In additional embodiments, the above method can
differentiate the (or is sensitive to) differences in the
concentration of a metal ion (e.g., silver ions) wherein the
difference in metal ion concentration is less than about 500 ppb,
less than about 250 ppb, less than about 100 ppb, less than about
50 ppb, or less than about 25 ppb. In other embodiments, the above
method, for example, can differentiate between a silver ion
concentration of about 5 ppb in one sample and a silver ion
concentration of about 100 ppb in another sample. In some
embodiments the emission color can be detected visually, or
spectroscopically. In other embodiments, the change in emission
color can be detected visually or spectroscopically.
[0109] In some embodiments, the sample comprises biological media.
In some embodiments, the sample comprises phosphate buffer, RPMI
media, or a combination thereof. In yet other embodiments, the
sample comprises silver ions and silver nanoparticles. In other
embodiments, the method can accurately sense the concentration of
silver ions in a sample comprising silver nanoparticles without
interference from the silver nanoparticles. In other embodiments
the method differentiates free silver ions (Ag.sup.-) from
nanosilver (Ag (0) particles. In other embodiments, the sample is
stabilized in biological media. In some other embodiments,
different concentrations of silver ions can be differentiated by
emission intensity.
[0110] In other embodiments, the sample is water wherein KCl is in
the water, and KCl in the water does not change or substantially
does not change sensing of silver ions in the mixture when the
concentration of silver ions in the sample is less than about 25
ppm, about 10 ppm, about 7 ppm, about 5 ppm, or about 3 ppm.
[0111] This disclosure provides ranges, limits, and deviations to
variables such as volume, mass, percentages, ratios, etc. It is
understood by an ordinary person skilled in the art that a range,
such as "number1" to "number2", implies a continuous range of
numbers that includes the whole numbers and fractional numbers. For
example, 1 to 10 means 1, 2, 3, 4, 5, . . . 9, 10. It also means
1.0, 1.1, 1.2. 1.3, . . . , 9.8, 9.9, 10.0, and also means 1.01,
1.02, 1.03, and so on. If the variable disclosed is a number less
than "number10", it implies a continuous range that includes whole
numbers and fractional numbers less than number10, as discussed
above. Similarly, if the variable disclosed is a number greater
than "number10", it implies a continuous range that includes whole
numbers and fractional numbers greater than number10. These ranges
can be modified by the term "about", whose meaning has been
described above.
Results and Discussion
[0112] Herein is reported the formation and chemosensory properties
of a phosphorescent complex, {[(3-CH.sub.3,5-COOH)Pz]Au}.sub.3 (aka
Au.sub.3Pz.sub.3) stabilized in a CS polymer matrix. This is
believed to be the first report in which a cyclic Au(I) trimer
complex showed in situ formation within an aqueous polymeric medium
while retaining phosphorescence features and also the first ever
gold complex capable of sensing sub-ppm levels of silver ions in
aqueous solution.
[0113] Evidence of formation of Au.sub.3Pz.sub.3. In addition to
photoluminescence data presented in the next section, the formation
of Au.sub.3Pz.sub.3 in solution was confirmed by .sup.1H-NMR,
ESI-MS, and FT-IR techniques. The photophysical measurements were
performed for both CS-stabilized and polymer-free samples of
Au.sub.3Pz.sub.3 in DI water (FIG. 1).
[0114] The .sup.1H-NMR spectrum of the PzH ligand shows a singlet
broad peak at 12.86 ppm, due to N--H proton resonances at the
1-position of the pyrazole ring. The ionization of the carboxylic
acid group (--COOH) renders no distinguishable peak of that proton.
Singlets at 6.440 ppm and 2.224 ppm can be attributed to the C4-H
and C3-CH.sub.3 protons on this substituted pyrazole. The
.sup.1H-NMR spectrum for Au.sub.3Pz.sub.3 (1) shows the
disappearance of the singlet broad peak at 12.86 ppm. This is
consistent with the formation of a coordinate-covalent bond between
the ligand and gold(I) via its nitrogen atoms (N--Au--N). All other
peaks from the ligand remained essentially intact with only minor
shifts in their resonances.
[0115] ESI-MS data showed distinguishable peaks for the ligand and
Au.sub.3Pz.sub.3. The calculated molecular weight for this ligand
is 126.0 g/mol, giving rise to m/z=125 in the negative mode of
ESI-MS. This fragmentation value indicates ligand deprotonation in
aqueous solution, [L-1H].sup.-=Pz.sup.-. The calculated molecular
weight of Au.sub.3Pz.sub.3 is 966.0 g/mol and since it has three
carboxylate groups substituted on three pyrazolate moieties,
fragmentation can be potentially around m/z=322 if all carboxylate
protons are lost. However, the spectrum shows no distinct peaks at
m/z=322 but a clear peak at m/z=965, [1-H].sup.-, indicates the
formation of a full trimeric unit of Au.sub.3Pz.sub.3. This ESI-MS
pattern suggests an ionization at one of the carboxylic groups
present in this complex as COO.sup.-, whereas the two other units
remain protonated (COOH), [Au.sub.3Pz.sub.3-H].sup.-.
[0116] The FT-IR spectrum of the ligand shows clear peaks at 3243
cm.sup.-1, 3151 cm.sup.-1, 1715 cm.sup.-1 and 1590 cm.sup.-1, which
are characteristic stretching bands for v(N--H), v(O--H),
v(C.dbd.O) and v(N--N). Comparatively, Au.sub.3Pz.sub.3 shows FT-IR
spectral bands at 3242 cm.sup.-1, 3139 cm.sup.-1, 1688 cm.sup.-1,
and 1529 cm.sup.-1 for the v.sub.N--H, v.sub.O--H, v.sub.C.dbd.O,
and v.sub.N--N stretching modes. As the reaction is not efficient
in polymer-free DI water, there are some residues of unreacted
ligand that showed a stretching band at 3242 cm.sup.-1 coming from
the N--H of uncomplexed PzH. The far-IR region of the gold
precursor, Au(THT)Cl, shows a stretching band at 326 cm.sup.-1 for
v.sub.Au--S, which disappears upon Au.sub.3Pz.sub.3 formation
concomitant with the appearance of new bands at .about.260 and
150-180 cm.sup.-1, which is attributed to v.sub.Au--N and
.delta..sub.N--Au--N based upon: a) comparison with multiple
experimental and/or computational literature precedents; and b)
experimental DFT calculations, relating to predicted IR spectra for
an unsubstituted Au.sub.3Pz.sub.3 model to the experimental IR data
and to the literature precedents.
[0117] Photophysical studies of Au.sub.3Pz.sub.3. Photophysical
properties were analyzed by comparing Au.sub.3Pz.sub.3 in polymer
vs DI water (polymer-free solution) to understand the effect of the
polymer on the formation and stability of Au.sub.3Pz.sub.3. FIG. 1
shows the differences in photophysical properties of
Au.sub.3Pz.sub.3 synthesized in the presence vs absence of CS
polymer in DI water. The appearance of the red emission band from
both systems is an indication of the formation of cyclic Au trimer
units and self-assembly of attractive intertrimer units by
aurophilic interactions involving adjacent units of
Au.sub.3Pz.sub.3, as known for linear Au(I) complexes in general
and such cyclotrimers in particular in both the solid state and
(albeit organic) solution.
[0118] Chart 1 shows the possible intertrimer aurophilic
interaction motifs of Au.sub.3Pz.sub.3 units that induce the
luminescence in both systems. The presence of the CS polymer not
only significantly enhances the formation of Au.sub.3Pz.sub.3 but
also promotes aggregation, which is speculated to be at least in
part due to ion-pairing the --COO.sup.- anionic groups by the
polymer --NH.sub.3.sup.+ groups to ameliorate electrostatic
repulsion between otherwise anionic trimer units. The emission and
excitation peak maxima for polymer-free aqueous Au.sub.3Pz.sub.3
(.lamda..sub.exc=305 nm and .lamda..sub.em=710 nm) is distinctly
different from Au.sub.3Pz.sub.3 (.lamda..sub.exc=290 nm and
.lamda..sub.em=690 nm) stabilized in CS polymer. Polymer-free
Au.sub.3Pz.sub.3 exhibits rather feeble red emission compared to
the bright red emission of Au.sub.3Pz.sub.3 synthesized in CS
polymer media (FIG. 1).
##STR00005##
[0119] The phosphorescence quantum yield and lifetime of
Au.sub.3Pz.sub.3 synthesized in polymer media were much higher
compared to Au.sub.3Pz.sub.3 synthesized in polymer-free aqueous
media (Table 1). In addition, in the CS matrix, Au.sub.3Pz.sub.3
showed dual-exponential lifetimes. While in polymer-free media,
Au.sub.3Pz.sub.3 exhibited rather weak emission with an
immeasurable absolute quantum yield and a single exponential
lifetime of .about.1 .mu.s, which was close to the time resolution
of the flash lamp used in the experiment. It is strongly believed
that these differences in photophysical properties of
Au.sub.3Pz.sub.3 in polymer vs polymer-free media could be due to a
combination of factors: (a) Presence of CS polymer results in
better stabilization and high-yield synthesis of Au.sub.3Pz.sub.3.
(b) The positively charged CS polymer causes ion-pairing
interactions with the tri-anionic monomer Au.sub.3Pz.sub.3 or,
hexa-anionic dimer-of-trimer [Au.sub.3Pz.sub.3].sub.2 units, which
stabilizes the complex, resulting in less excited state distortion
(emission peak maxima at 690 nm vs 710 nm, respectively). (c) The
reduction of the surface charge from +62.7.+-.4.2 mV for free CS to
+50.1.+-.3.3 mV for the CS-stabilized Au.sub.3Pz.sub.3 sample
represents direct evidence of the aforementioned ion-pairing
interactions. (d) Lastly, the presence of the CS polymer
significantly reduces the access of water and oxygen quenching
molecules to the Au.sub.3Pz.sub.3 chromophore, resulting in both
enhanced luminescence and increased stability.
[0120] The stability effect of the polymer on the microenvironment
is evident from the dual-lifetime behavior of Au.sub.3Pz.sub.3
(FIG. 1). In fact, Au.sub.3Pz.sub.3 samples synthesized in the
polymer are stable up to a few months without compromising their
photophysical properties, whereas polymer-free
aqueous-Au.sub.3Pz.sub.3 decomposes in a few hours.
Au.sub.3Pz.sub.3 in CS also exhibits excellent stability against
degradation from photobleaching in solution (FIG. 8), with less
than 7% change in emission signal after 4 hours of irradiation,
suggesting a significant role of the polymer in photostability.
This type of behavior is not unusual and there are on enhanced
stability and brightness of fluorescent or phosphorescent molecular
systems when incorporated into polymers and polymer nanoparticle
matrices.
TABLE-US-00001 TABLE 1 Summary of Photophysical Properties of
Au.sub.3Pz.sub.3. Sample Form .tau. (.mu.s) .PHI..sub.PL
Au.sub.3Pz.sub.3/H.sub.2O Soln. <1 .mu.s N/A Au.sub.3Pz.sub.3/CS
Soln. 14.24 .+-. 0.16 (25%) 0.05 .+-. 0.01 3.84 .+-. 0.23 (75%)
Au.sub.3Pz.sub.3/CS Film 14.19 0.48 .+-. 0.05
Au.sub.3Pz.sub.3/CS/Ag.sup.+ Soln. 13.92 .+-. 0.08 0.198 .+-. 0.02
Au.sub.3Pz.sub.3/CS/Ag.sup.+ Film 10.81 0.11 .+-. 0.03
[0121] Selective sensing of silver with Au.sub.3Pz.sub.3. Silver
ion sensing with Au.sub.3Pz.sub.3 was carried out by titration
experiments at RT. Typical steady-state emission and excitation
spectra of the Au.sub.3Pz.sub.3/Ag.sup.+ adduct in polymer media at
pH .about.6.5 are shown in FIG. 2. The excitation peak for the
Au.sub.3Pz.sub.3/Ag.sup.+ adduct solution is at
.lamda..sub.max=305-325 nm while the emission peak is at
.lamda..sub.max=470-510 nm with the variation depending on the
concentration of silver ions. Upon addition of silver into
Au.sub.3Pz.sub.3, a new distinct blue-shifted emission peak appears
at .lamda..sub.max=515 nm with an albeit red-shifted excitation of
.lamda..sub.max=325 nm, representing a drastic reduction in Stokes'
shift by .about.8,830 cm.sup.-1 (from 19,990 cm.sup.-1 to 11,160
cm.sup.-1) vs Au.sub.3Pz.sub.3 alone. The red emission peak at
.about.685 nm of Au.sub.3Pz.sub.3 diminishes slowly and essentially
disappears after adding 250 .mu.M of silver ions.
[0122] The photophysical properties observed for the
Au.sub.3Pz.sub.3/Ag.sup.+ adduct are, therefore, drastically
different from those for Au.sub.3Pz.sub.3 alone. The extremely
bright green-emissive solution of Au.sub.3Pz.sub.3/Ag.sup.+ shows a
single exponential lifetime .tau.=13.92.+-.0.08 .mu.s and a quantum
efficiency .PHI.=0.19.+-.0.02 at RT without deaeration. The red
shift in the excitation maxima and blue shift in the emission
maxima upon addition of silver ions are similar to the changes
observed by Burini et al. (Inorg. Chem. 2003, 24, 253) and Aida et
al. (J. Am. Chem. Soc. 2005, 127, 179) in solid-state and organogel
media. Upon silver sandwiching by Au.sub.3Pz.sub.3 trinuclear
complexes, the [Au(I)].sub.3 . . . Ag(I) . . . [Au(I)].sub.3
interaction becomes remarkably strong in the ground state, more so
than the Au(I) . . . Au(I) intertrimer interaction, which causes
the red-shift in excitation.
[0123] Likewise, photoexcitation to the phosphorescent state of the
Au.sub.3Pz.sub.3/Ag.sup.+ sandwich adduct will undergo a smaller
Stokes' shift than that for the transformation of intertrimer Au(I)
. . . Au(I) interactions to excimeric .sup.3[Au(I)--Au(I)]*
covalent bonds, because of the strong ground-state metal-metal
bonding for Au(I) . . . Ag(I). Aida et al. have shown that the
emission color tunability can be achieved by the addition of silver
ions to gold(I) pyrazolate trimer complexes composed of long alkyl
chains in organic media, due to the formation of organogels. In the
solid state, emission color tunability due to intercalation
(sandwich type structure) of heavy metal ions between trimer units
has been demonstrated. Likewise, the formation of a similar half-
or full-sandwich structure between one or two units of
Au.sub.3Pz.sub.3, respectively, and the heavy metal ion, (Ag.sup.+
in particular and, to a lower extent, Tl.sup.+, Pb.sup.2-, or
Gd.sup.3+) that results in emission tunability and sensing behavior
from the trinuclear gold(I) pyrazolate complex, is proposed. It is
also assumed that along with the formation of a sandwich structure,
ionic interactions between heavy metal cations and the carboxylated
functional groups presented in Au.sub.3Pz.sub.3 can further assist
the formation of an emission tunable adduct; see Chart 1 (C).
[0124] In order to understand the selective sensitivity to
Ag.sup.+, Au.sub.3Pz.sub.3 was separately titrated with 15
different metal ions, each at a constant salt concentration of 4.97
.mu.M. Upon individual titration of metal ions besides Ag.sup.+,
the PL spectrum remained unchanged. Only after addition of silver
salt did a new PL band at 475 nm evolve (FIG. 3A). FIG. 3A shows
that upon individual titration of 15 other metal ions, the
Au.sub.3Pz.sub.3 emission baseline at 475 nm was unaltered. There
is a 15-fold emission enhancement from the baseline at 475 nm only
in the presence of Ag.sup.+ (FIG. 3B). The I/I.sub.0 values in FIG.
3B confirm that Au.sub.3Pz.sub.3 is extremely and selectively
sensitive to Ag.sup.+ at .about.5 .mu.M levels. At such low
Ag.sup.+ concentrations, however, the new bright-green emission
peak at 475 nm is concomitant with the red PL at 690 nm, indicating
the presence of both sandwiched and non-sandwiched units of Au
cyclotrimer.
[0125] After understanding the selectivity of Au.sub.3Pz.sub.3 for
silver ions, the interference effect of other metal ions on the
sensitivity of silver was also investigated. At a fixed
concentration (4.97 .mu.M), all other metal cations were first
added sequentially to the same solution of Au.sub.3Pz.sub.3. The
order of addition is indicated in FIG. 9 and the emission spectrum
was recorded after addition of each metal ion. It can be clearly
noticed that even by this titration process, only after the
addition of silver salt the evolution of a new emission peak at 475
nm (FIG. 9A) was observed. Further, I/I.sub.o values for silver
addition did not appreciably change even in the presence of all the
different metal ions in solution. This result shows that the
selective detection of Ag.sup.+ by the Au.sub.3Pz.sub.3
phosphorescent chemosensor for Ag.sup.+ is immune to interference
from other metals salts at .about.5 .mu.M concentrations.
[0126] Detection Limit for Silver Sensing by Au.sub.3Pz.sub.3.
After understanding the selectivity of Ag.sup.+ sensing by
Au.sub.3Pz.sub.3, the detection limit and a measurement range of
Au.sub.3Pz.sub.3 for silver were determined from titration
experiments. FIG. 4A shows PL titration data for Au.sub.3Pz.sub.3
by gradual addition of silver salt (0.fwdarw.11 ppm) at pH
.about.6.5 and RT. These data demonstrate a stepwise sensitization
of the 475 nm PL peak, whereas the 690 nm peak exhibits gradual
quenching. The detection limit and measurement range were
determined at two polymer concentrations, 0.1 and 1.0 w/v % CS.
[0127] The detection limit was calculated using two methods,
S/N>3 (signal-to-noise ratio) and a threshold of 10% increase in
PL intensity vs the sensor's signal, and the analysis is done
without (Table 2 and FIG. 4) and with (Table 3 and FIGS. 11-13)
baseline correction by subtracting the latter signal. The detection
limit based on S/N>3, without baseline correction, varied
between 1.5 and 0.5 ppm depending on w/v % of CS (Table 2), whereas
these values improved by 3 orders of magnitude to ppb/nM levels
upon careful manipulations of baseline correction, attaining 6-37
ppb detection limits (Table 3 and FIGS. 11-13).
[0128] Au.sub.3Pz.sub.3 synthesized at a lower concentration of CS
sensed as low as 5 ppb added aliquots (FIG. 10 and Table 2).
Au.sub.3Pz.sub.3 synthesized at 1.0% and 0.1% CS exhibits a
detection limit (based on 10% signal change) of 0.5 ppm and 20 ppb,
respectively, without baseline correction (Table 2 and FIG. 4B),
which improved to 40 ppb and 14 ppb, respectively, upon appropriate
baseline correction (Table 3 and FIGS. 11-13). Thus, FIG. 4B data
suggest that the concentration of CS has a clear effect not only on
the detection limit but also on the measurement range of
Au.sub.3Pz.sub.3, which varied within <0.5-9.3 ppm at the higher
1.0 w/v % CS while the lower 0.1 w/v % CS reduced the upper limit
to 7.0 ppm and lower limit to 5 ppb.
[0129] Tabular forms detailing all of the sensitivity parameters
for various titrations are listed in Table 2 and Table 3. The
addition of silver ions beyond the measurement range of the sensor
resulted in a peak shift from 470 to 510 nm. It is hypothesized
that this continuous red-shift in emission noticed in FIG. 4A with
respect to incremental addition of silver ions is likely due to a
change from a half-sandwich to a full-sandwich adduct between
Ag.sup.+ and one or two units of Au.sub.3Pz.sub.3, respectively,
with the gradual red-shifting for each adduct resulting from
conformational changes that increase the extent of Ag(I)--Au--(I)
overlap. A similar rise of a new PL peak at 475 nm using 285 nm
excitation (FIG. 14) was also noticed. The interaction of Ag.sup.+
with Au.sub.3Pz.sub.3 is confirmed from a Job plot (FIG. 15).
[0130] The profile of the Job plot titration suggests an
equilibrium between a 1:2 and 1:1 interactions of silver ions with
Au.sub.3Pz.sub.3, corresponding to full- and half-sandwich adduct
formation, respectively, with a slight preference for the former
(.about.1.2 peak ratio), as shown in FIG. 15, substantiating the
aforementioned hypothesis. Lastly, the reversibility of Ag.sup.+
sensing was investigated by using the well-known chelating agent,
EDTA=ethylenediaminetetraacetic acid, as shown in FIG. 5. The
process was repeated for 3 cycles using various Ag.sup.+ and EDTA
concentrations, which tuned the reversibility. A detailed study to
assess the reversibility across the entire measurement range of the
sensor is under investigation. However, these preliminary results
have indicated that Au.sub.3Pz.sub.3 can be used as both a reusable
sensor and as a scavenger of silver ions depending on the
concentration of both Ag.sup.+ and EDTA, which may be helpful for
addressing toxicity concerns of Ag.sup.+.
TABLE-US-00002 TABLE 2 Detail of the sensitivity numbers for
various CS concentrations. Detection Detection Detection Range
Studied Incremental Range Limit Type Sample (ppm) (ppm) (ppm) (ppm)
S/N > 3 High w % 0 to 11 0.52 0 to 9.3 Less than 1.58 10% Signal
CS Less than 0.5 Change ppm S/N > 3 Low w % 0 to 2.2 0.005 Less
than 0.5 10% Signal CS Less than 0.02 Change ppm S/N > 3 Low w %
0 to 11 1.5 0 to 7 Less than 0.5 CS ppm 10% Signal NA Change High w
% Polymer Low w % Polymer Low w % Polymer PPM (Ag.sup.+) I/I.sub.0
PPM (Ag.sup.+) I/I.sub.0 PPM (Ag.sup.+) I/I.sub.0 0 1 0 1 0 1
0.53179 1.83428 0.00545 1.02017 0.53 4.94034 1.0593 2.74389 0.0109
1.04789 2.09 1.35E+01 1.58039 3.72524 0.01635 1.06825 3.61 1.91E+01
2.0972 4.73677 0.0218 1.10698 5.09 2.18E+01 2.60973 5.45351 0.02725
1.13674 7 2.28E+01 3.11584 6.46364 0.03259 1.19566 8.83 2.15E+01
3.61767 7.17085 0.03793 1.38898 11.03 1.84E+01 4.11522 7.68619
0.04338 1.44482 4.60742 8.38462 0.04796 1.44547 5.09427 9.08925
0.05341 1.46022 5.57791 9.50001 0.10791 1.77106 6.0562 9.9181
0.26585 2.6495 6.53021 10.49448 0.51905 4.0687 6.99994 11.0518
0.99081 6.64684 7.46432 11.39824 2.18 12.35116 7.92549 11.6384
8.38238 12.09288 8.83392 12.77916 9.28225 13.58009 9.63963 13.50043
10.16714 13.44599 10.60263 13.55038 11.03491 13.57211
TABLE-US-00003 TABLE 3 (a) Sensitivity parameters for Ag.sup.+
detection by the Au.sub.3Pz.sub.3/CS phosphorescent sensor at
various CS concentrations, upon baseline correction of the raw data
- corresponding to the data summarized in Tables 3b-3d below and
FIGS. 11-13 (FIGS. 11a-13a, S/N > 3 method; 11b-13b, 10%
method). Detection Detection Range Studied Increment Range Limit
Detection Type Sample (ppm) (ppm) (ppm) (ppb) S/N > 3 1.0% CS 0
to 11 0.52 0 to 9.3 37 10% Signal 40 Change S/N > 3 0.1% CS 0 to
2.2 0.005 0 to 2.2 6.4 10% Signal 14 Change S/N > 3 0.1% CS 0 to
11 1.5 0 to 7 8.2 10% Signal 72 Change
(b) Summary of PL intensity raw data and manipulation thereof used
for the sensitivity parameters calculations in Table 3a for the
1.0% CS/0-11 ppm data. The bottom cluster of rows (16-21) was
chosen for inclusion in Table 3a, given it most-accurately
represents the pertinent noise level (FIG. 11a).
TABLE-US-00004 Row X (nm) Y (N) Y (S) Y (S - N) N N * 3 1 401
185456 177613 -7843 16054 48162 2 402 183350 180212 -3138 3 403
179491 181023 1532 6.827038 S/(N * 3) 4 404 176824 185035 8211 0.52
ppm (conc. @ S) 5 470 92086.2 420890 328803.8 S (0.52 ppm) 0.07617
Detection limit (ppm) 6 76.1677 Detection limit (ppb) 7 8 383
165260 160784 -4476 16631 49893 9 384 167117 169281 2164 10 385
167453 175125 7672 11 386 164815 176970 12155 S (0.52 ppm) 6.590179
S/(N * 3) 12 470 92086.2 420890 328803.8 0.52 ppm (conc. @ S) 13
0.07891 Detection limit (ppm) 14 78.9053 Detection limit (ppb) 15
16 17 366 50269.5 50971 701.5 7767.4 23302.2 18 367 54913.3 63382.2
8468.9 S (0.52 ppm) 14.11042 S/(N * 3) 19 470 92086.2 420890
328803.8 0.52 ppm (conc. @ S) 20 0.03685 Detection limit (ppm) 21
36.8522 Detection limit (ppb)
(c) Summary of PL intensity raw data and manipulation thereof used
for the sensitivity parameters calculations in Table 3a for the
0.1% CS/0-2.2 ppm data. The italic rows with values were chosen for
inclusion in Table 3a, given it most-accurately represents the
pertinent noise level; see FIG. 12a.
TABLE-US-00005 Row N N*3 1 2712.2 8136.6 2 9081 27243 3 486 nm
(peak max) 4 S-N 67414.9 5 S-N 67414.9 6 S/N*3 8.285389475 7 S/N*3
2.474576956 8 0.05341 ppm addition 9 0.05341 ppm addition 10
0.00645 Det. Limit (ppm) 11 6.44629 Det. Limit (ppb) 12 0.021583
Det. Limit (ppm) 13 21.58349 Det. Limit (ppb)
(d) Summary of PL intensity raw data and manipulation thereof used
for the sensitivity parameters calculations in Table 3a for the
0.1% CS/0-11 ppm data. The italic rows with values were chosen for
inclusion in Table 3a, given it most-accurately represents the
pertinent noise level; see FIG. 13a.
TABLE-US-00006 Row High Noise 1 N 3N 2 5551 16653 3 479 nm S (max)
(peak max) 4 140261 724650 584389 5 S/(N*3) ppm (S) 6 35.09211553
0.52 7 0.014818143 ppm 8 14.81814339 ppb 9 Low Noise 10 N 3N 11
578.5 1735.5 12 S/(N*3) ppm (S) 13 336.7265918 0.52 14 0.00154428
ppm 15 1.544279581 ppb 16 Reported value (average hi & low
noise) 17 0.008181211 ppm 18 8.181211488 ppb
[0131] Sensing of other heavy-metal ions with Au.sub.3Pz.sub.3. It
is evident from FIG. 3 and FIG. 4 that, at low concentrations
(.ltoreq.5 .mu.M), Au.sub.3Pz.sub.3 is only sensitive to silver
ions among the 15 salts tested. Nevertheless, at much higher
concentrations, Au.sub.3Pz.sub.3 exhibits sensitivity to thallium
at 85 mM TlNO.sub.3 by developing a new blue emission (PL maximum
at 450 nm with 315 nm excitation) as shown in FIG. 6. The lifetime
of the Au.sub.3Pz.sub.3/Tl.sup.+ adduct was .tau.=0.907.+-.0.06
.mu.s, significantly reduced vs Au.sub.3Pz.sub.3 alone. Further,
the PL of the thallium adduct is blueshifted compared to the silver
adduct. Au.sub.3Pz.sub.3 also shows a similar response for lead
ions at concentrations higher than 100 mM by developing a new
emission peak at 490 nm with excitation at 338 nm (FIG. 6). This
cyan PL color for the Au.sub.3Pz.sub.3/Pb.sup.2+ adduct is,
therefore, qualitatively different from that for
Au.sub.3Pz.sub.3/Ag.sup.+ or Au.sub.3Pz.sub.3/Tl.sup.+ adducts.
[0132] The PL spectral profiles show that there is no interference
or overlap of emission maxima between the different heavy-metal ion
adducts (FIG. 6 and FIG. 16). Although there is uncertainty about
the exact mechanism of sensing with different metals, it is assumed
the differences in supramolecular interactions between different
metals result in different emission colors. The results presented
in this paper indicate the origin of sensitivity to Tl.sup.+ and
Pb.sup.2+ only at relatively higher concentrations compared to
Ag.sup.+. On the basis of measurement range results of silver,
however, it is believed that fine-tuning the wt % of CS polymer can
aid in improving the sensitivity to Tl.sup.+ and Pb.sup.2+, as can
be developed for Au.sub.3Pz.sub.3 and related trimers.
[0133] The other metal investigated was trivalent gadolinium, which
has been primarily explored for bioimaging applications. FIG. 6
shows the PL spectrum of the Au.sub.3Pz.sub.3/Gd.sup.3+ adduct.
Upon addition of Gd.sup.3+ ions (0.7 mM), a new weaker emission
peak appeared at 468-470 nm under .lamda..sub.exc.about.320-400 nm,
along with an enhancement in the red emission under
.lamda..sub.exc<300 nm, the latter result being unusual as all
other ions have exhibited quenching in the red emission of
Au.sub.3Pz.sub.3. The lifetime of the Au.sub.3Pz.sub.3/Gd.sup.3+
complex at 320/470 nm shows a single-exponential long lifetime
.tau.=16.61.+-.0.25 .mu.s, indicating the newly evolved peak in the
presence of Gd.sup.3+ is due to the formation of an
Au.sub.3Pz.sub.3/Gd.sup.3+ adduct.
[0134] It was also found that, upon mixing the red emissive
Au.sub.3Pz.sub.3, green emissive silver adduct, and blue emissive
thallium adduct, a nearly white emissive mixture (FIG. 6) is
obtained that exhibits a broad emission ranging from blue to red.
This could be significant for solid-state lighting and/or video
display applications associated with color mixing, including white.
However, the spectra are not additive, as the
Au.sub.3Pz.sub.3/Tl.sup.+ adduct emission appears red-shifted in
the presence of Ag.sup.+; further optimization can attain suitable
color metrics for such applications. In general, the sensitivity
and selectivity of the Au.sub.3Pz.sub.3 sensor seem to favor the
softer cations, consistent with the data in FIG. 6. In FIG. 17, the
normalized emission spectra illustrate noninterference from the
chitosan-pyrazole control, as does FIG. 11 for the baseline
correction even at minute aliquot addition of Ag ions.
[0135] The film-forming ability of CS to investigate potential
chemosensor films, as such films are more conducive to subsequent
investigations to develop practical sensors (e.g., fiber-optic
sensors and sensor stripes) has been exploited. Accordingly, thin
films were fabricated from Au.sub.3Pz.sub.3 and
Au.sub.3Pz.sub.3/Ag.sup.+ solutions by a simple drop-cast method.
FIG. 7 and Table 1 provide details of the photophysical properties
of the red-emissive and green-emissive thin films in comparison
with the same systems in solution. FIG. 7 shows that the
Au.sub.3Pz.sub.3 film possesses a much higher quantum yield (see
FIG. 18 for PL and QY data) compared to the
Au.sub.3Pz.sub.3/Ag.sup.+ silver adduct film, opposite to the
solution behavior. In the case of films, Au.sub.3Pz.sub.3 has shown
a drastic increase in quantum yield due to common solid-state
behavior of Au(I) complexes, which exhibit better orientation and
higher degree of intermolecular aurophilic aggregation required for
their luminescence vs the solution phase. The silver adduct, on the
other hand, exhibits a slight decrease in lifetime and quantum
yield in the solid film vs solution. Stronger metal-metal bonding
exists in the sandwich adduct vs the aurophilic dimer (e.g.,
d.sub.Ag--Au.about.2.9 .ANG. in such adducts vs>3.3 .ANG. for
intertrimer d.sub.Au--Au in uncomplexed trimers). This is expected
to lead to greater survival chances for the
Au.sub.3Pz.sub.3/Ag.sup.+ adduct in solution, whereas its further
solid-state aggregation could attain self-quenching.
[0136] Conclusions: Reported herein is a chemo-optical sensor based
on a novel phosphorescent Au(I) cyclotrimer complex
(Au.sub.3Pz.sub.3=[Au(3-CH.sub.3,5-COOH)Pz].sub.3) that is
extremely selective and sensitive to silver ions in aqueous media.
The Au.sub.3Pz.sub.3 is unconventionally synthesized in chitosan
(CS) aqueous media and its photophysical and sensing properties are
analyzed in detail. The chemo-optical sensor exhibits sub-ppm/nM
range sensitivity for silver ions, whereas thallium and lead ions
were also detected at micromolar concentrations. The presence vs
absence of silver ions in aqueous polymer media was differentiated
from starkly distinct differences in emission wavelengths,
lifetimes and quantum yields of Au.sub.3Pz.sub.3 vs the
Au.sub.3Pz.sub.3/Ag.sup.+ adduct. Selectivity, sensitivity,
measurement range, and detection limit data all demonstrate room
for optimization and for improvement in sensitivity for silver and
other heavy metal ions using the same chemosensor and congeners
thereof. This is believed to be the first documented silver sensing
methodology by an Au(I) phosphorescent complex in the presence of
(e.g., 15) other metal salts. Based on these results, it is
believed that this heavy metal chemosensor possesses a great
potential for practical applications such as detection of silver
ions in drinking water or surface water (rivers, lakes reservoirs,
etc.) and also in solution-processed functional light-emitting
devices.
Ratiometric Phosphorescent Silver Sensor: Detection and
Quantification of Free Silver Ions Within Silver Nanoparticles
[0137] One of the largest sources of silver contamination is from
engineered silver nanoparticles (AgNPs). Especially in the last
decade, AgNPs have become very common in many commercially
available products such as bedding, toothpaste, bandages, fabrics,
deodorants, kitchen utensils, and toys--due to their known
antibacterial properties. In addition, scientists further take
advantage of the antibacterial properties of AgNPs by using them in
other applications such as pharmacology, human and veterinary
medicine, food industry, and water purification. The interest in
using AgNPs as an antibacterial agent comes from the fact that
certain bacteria such as MRSA are becoming resistant to
antibiotics. The potential for silver as an alternative to
antibiotics is due to the many studies showing silver's
effectiveness on a wide range of bacteria. The potential mechanism
of silver's antibacterial properties involves their accumulation in
bacterial cells, resulting in shrinkage of the cytoplasm membrane
and detachment from the cell wall. Therefore, DNA molecules become
condensed and lose their ability to replicate.
[0138] Unfortunately, it is a known issue that silver ions are
toxic to humans because silver can be absorbed through the lungs,
gastrointestinal tract, mucous membranes, and skin. Studies have
shown that there has not been any documented beneficial/essential
physiological or biochemical role for silver in the human body.
Excessive silver ion intake can lead to the long-term accumulation
of insoluble precipitates in the skin, eyes, and other
organs--causing various medical conditions. Therefore, the release
of various silver species (silver nanoparticles and different
silver salts) into the environment from multiple sources and
applications is concerning. Understanding the toxic effects of free
silver salts is arguably straight-forward and easily studied.
However, studying the toxicity mechanism of AgNPs to various
biological systems is not quite clear. This challenge is due to the
dynamic transformation of AgNPs to silver ions upon interacting
with the media. The chemical and morphological changes of AgNPs
makes it difficult to understand the exact mechanism of toxicity of
AgNPs in different media. Therefore, one important step would be
the ability to differentiate the free silver ions leaching or the
silver ions chemically transformed from AgNPs so that the toxicity
specifically due to free silver ions vs AgNPs can be clearly
understood.
[0139] Due to the fact that different NPs under different
conditions (such as pH, size, and chemical composition) could
greatly alter the physiochemical and morphological properties and
thereby the toxicity of the AgNPs, it is important to characterize
silver leaching in the specific environment of that particular
application. The challenge of understanding the role of different
species in different media can be made very easy if each of these
species could be isolated and quantified. Currently, a combination
of field flow fractionation (FFF) and inductively coupled plasma
mass spectrometry (ICP-MS) are adapted in a combination with
various other detectors to determine size and quantification of
AgNPs in aqueous matrices.
[0140] Other combinations of detectors include simple UV-Vis
spectrophotometer, centrifugal ultrafiltration and diffusive
gradients for detection and separation of AgNPs based on their
surface plasmon resonance and size. Additionally, there are
numerous well-known approaches to quantify the silver ion
concentration down to the part-per-billion (ppb) level. These
techniques include atomic absorption (AA) spectroscopy, ICP-MS, and
potentiometric methods based on ion-selective electrodes. Most of
these methods are time-consuming, expensive and unable to
differentiate AgNP from silver ions. Also, the sample preparation
needed for these methods can induce changes to the properties of
the AgNPs, which introduces uncertainty in the subsequent
analytical results. These AgNPs modifications can create a large
gap for understanding the actual interactions of different silver
species in the environment and in biological systems. However,
luminescent indicators are advantageous due to their high
sensitivity, rapid response, and ease of use.
[0141] Nonetheless, there is still a challenge in quantifying the
exact concentration of silver ions to the ppb level--even in the
presence of silver nanoparticles--without sacrificing the AgNPs
sample. This disclosure documents the development of an optical
sensor sensitive to silver ion concentration in aqueous chitosan
(CS) matrix down to the ppb range, and that uniquely identifies
silver and differentiates free silver ions from AgNPs. Further, the
ability of the sensor for sensing silver ions is not crippled in an
AgNP medium. This differentiation between the AgNPs and silver ions
is the first step towards determining the exact role of different
silver species in terms of their relative contribution to the
toxicity of AgNPs. Additionally, as discussed above, the same
system has already demonstrated that the sensitivity of the sensor
is not affected by the presence of other inorganic salts in the
aqueous medium. In addition, this sensor can detect the leaching of
silver ions from AgNPs over time, as well as being able to
remediate these ions from solution.
Results and Discussion
[0142] AuT selectivity for Ag.sup.+ ions: The synthesis,
characterization and photoluminescence properties of the cyclic
pyrazolate trimer have been extensively delineated, as discussed
above. The changes in emission color of the Au(I)-pyrazolate trimer
(AuT) from red (690 nm) to green (475 nm) in the presence of silver
ions has been demonstrated using the same complex, as discussed
above. The factors affecting the green emission at 475 nm in the
presence of silver and its detection limits in different polymer
concentrations were also clearly documented. Additionally, this
disclosure shows that the selectivity and sensitivity of the trimer
for silver ions is not affected by the presence of numerous other
inorganic salts. Realizing the significance of differentiating the
presence of silver ions vs AgNPs, the first step was to ensure that
the sensor only responds to free silver ions (monovalent Ag.sup.-
form) and not the AgNPs (zero-valent Ag(0) form) in solution.
[0143] The photoluminescence (PL) spectra and emission color
changes of the samples in FIG. 19A demonstrate the capability of
the sensor to selectively detect free silver ions and differentiate
those silver ions from AgNPs. The figure shows that upon addition
of 0.01 mg of 100 nM AgNPs to AuT, a very minor change in the PL
spectrum of the AuT complex is observed. The rise of a weak
emission shoulder at 475 nm is due to the interaction of AuT with
small amounts of free silver ions in the AgNPs solution.
Comparatively, the results show that upon addition of the same
concentration of Ag.sup.+ ions (0.01 mg), a distinct green emissive
peak is formed which is 4.times. more intense than the AgNPs
emission response. The inset pictures clearly show that the samples
containing silver ions vs AgNPs are easily differentiated when
excited with a hand-held UV lamp. This represents strong evidence
that the AuT sensor exhibits formation of a green-emitting sandwich
adduct described in ref 15. This allows for easy differentiation
and quantification of free silver ions from AgNPs in solution
without additional sample preparation. As discussed above, this
disclosure establishes that the peak maxima of Ag.sup.+--AuT
sandwich adduct's green emission exhibit a minor shift from 475 nm
to 500 nm at higher concentrations of free silver (Anal. Chem.
2018, 90, 4999).
[0144] Upon close comparison of the silver adduct peak maximum in
both the AuT+AgNPs and AuT+Ag.sup.+ solutions (FIG. 19A), a
noticeable shift from 475 nm to 500 nm is observed. The 475 nm peak
maximum corresponding to the silver adduct peak in the AgNP
solution indicates the presence of an insignificant amount of free
silver ions in the AgNP solution. This is expected based upon the
stability and continuous chemical transformations of AgNPs in
solution. However, in the presence of free silver ions of the same
concentration, the silver adduct exhibits an emission peak maximum
at 500 nm with a much higher PL intensity, indicating a much higher
concentration of free silver ions. This result is very significant
because it suggests AuT's selectivity to free silver ions vs AgNPs.
Additionally, it suggests the ability of the sensor to detect very
low concentrations of silver ions in an NP medium--undisturbed by
the presence of AgNPs. The blue color noticed in the inset picture
(FIG. 19) is the background interference arising from the 1 wt % CS
polymer that mediates the in-situ synthesis of AuT. The inset
pictures and the spectra clearly show that the CS polymer does not
affect the silver sensing of the AuT system.
[0145] In order to more precisely understand the interference of
AgNPs on sensing free silver ions, two different titration
experiments were conducted, as shown in FIG. 19B. The square dotted
line in FIG. 19B represents data for the addition of free silver
ions to an existing aliquot of AuT/AgNPs solution, while the round
dotted line represents the addition of AgNPs to an existing
solution of AuT/Ag.sup.+. The x-axis clearly shows that in both
cases, the same amount of silver (free silver or AgNPs) was added
to the AuT complex. The continuous increase in the intensity of the
475-nm peak for the free silver titration graph (square dotted
line), clearly indicates the continuous complexing of AuT with free
silver ions even in the presence of AgNPs. On the other hand,
except for the first Ag.sup.- addition, the 475 nm PL signal
remains constant during the AgNP titration experiment. This result
clearly indicates the sensor's selectivity for free silver ions
even in the presence of AgNPs. If this sensor were equally
sensitive to both Ag.sup.- ions and AgNPs then both the square and
round dotted lines would overlap with each other. The weak response
of the sensor to the AgNPs addition (round dotted line) could be
due to the presence of free silver ions in AgNPs solution, as
noticed in FIG. 19A.
[0146] Sensing Ag.sup.| ion leaching from AgNPs: Now that it has
been established that this sensor only detects free Ag.sup.+ ions
in solution, the ability of the sensor to determine the
leakage/leaching of silver from AgNPs in solution over time was
evaluated. The chemical transformation of AgNPs into various silver
species is one of the most challenging aspects for clearly
understanding the toxicity of AgNPs in the environment. Information
regarding the release or leakage of silver ions from AgNPs would be
extremely helpful in this respect. FIG. 20A illustrates the AuT
sensing of silver leaching/leakage from AgNPs over time. The same
concentration of 20 nM AgNPs was titrated into the sensor on day-1,
day-21, and day-35. Between experiments, the AgNPs were stored at
room temperature and under ambient light to promote
leaching/leakage of silver ions.
[0147] Based on FIG. 20A, the increase in I/I.sub.0, indicates the
leakage of silver ions from AgNPs over time. In addition, changes
in the AgNP properties (surface plasmon resonance (SPR), stability,
and aggregation) were monitored using UV-Vis data as collected
throughout the experimental time period. FIG. 20B shows the changes
in the SPR of the 20 nM AgNPs sample on day-1, day-21, and day-35,
respectively. FIG. 20B clearly shows a decrease in absorbance of
the AgNPs that would result either from a partial transformation of
AgNPs to silver ions or from the aggregation of the AgNPs. The
increase in the full-width-at-half maximum (FWHM) of the SPR peak
from 2757 cm.sup.-1 to 3122 cm.sup.-1 over the course of the
experiment clearly indicates that AgNPs were aggregating. In
addition, the shift in peak max from 394 to 399 nm is another
indication of aggregation. This is to be expected since the AgNP
samples were not stored properly in order to maximize their
stability, given the necessity to accelerate their aggregation or
decomposition for this study. However, from FIG. 20A the increase
in silver ion concentration due to the transformation of AgNPs is
clearly indicated by the increase in I/I.sub.o.
[0148] Based on these data, it can be concluded that the AgNP
samples were aggregating as well as leaching silver ions. Further
studies are warranted to determine how this aggregation affects
silver ion leaching. An advantage of this sensor is the ability to
use simple UV-Vis data to understand the physical and chemical
changes of the AgNPs. In the absence of such a straight-forward and
cost-effective optical sensor, the analysis of silver leakage would
require the use of ICP-MS or AA instrumentation with rigorous
sample preparation that compromises the sample quality in terms of
representing the identity of its silver species constituents. These
data clearly indicate the ability of the sensor to detect the
leakage of silver ions from AgNPs. Also, in combination with simple
UV-Vis spectroscopy, the sensor can help one understand the aging
and decomposition of AgNPs, which involves the aggregation of AgNPs
and/or release of free silver ions.
[0149] Next investigated was the sensor's ability to detect and
differentiate the presence/absence of free silver ions after
dialyzing the AgNPs (FIG. 21). After sensing the initial silver
content in the AgNPs (square dotted line in FIG. 21A), the AgNPs
were then placed in dialysis tubing (3000 Da) and dialyzed for 7
days. After this dialysis, the silver content of the AgNP solution
was retested and showed a drastic decrease in the sensor's
response--indicating the presence of very minute quantities of free
silver ions that were not removed during dialysis (FIG. 21A). It is
believed that there is a dynamic equilibrium between AgNPs and free
silver ions; therefore, further removal of silver ions was not
possible even by dialysis.
[0150] Along with the PL data, UV-Vis spectra were also acquired
for the AgNPs before and after dialysis. Initially, the UV-Vis data
could seem to apparently contradict the PL data; however, this is
not the case. Specifically, according to the UV-Vis data, there was
no change in the AgNP concentration, size or stability before and
after dialysis. However, these PL data show rather clearly that the
sensor has the potential to identify very small concentrations of
free silver ions that are associated with the AgNPs. These data
show the advantage of the disclosed silver sensor over conventional
AgNP characterization techniques such as UV-Vis. Specifically,
AgNPs have very high extinction coefficients; consequently, sensing
small changes in AgNP concentration is very difficult. In addition,
the dialysis water was also tested for the presence of silver
ions.
[0151] No silver ions were sensed within the dialysis water itself
due to the extremely small concentration of silver ions removed
from AgNPs. Therefore, sensing such a small concentration of silver
ions would prove challenging even to extremely sensitive techniques
such as AA. These data illustrate the advantage of the disclosed
sensor in that it is able to detect small changes in silver
concentration within an AgNP medium where common techniques like
UV-Vis and AA are unable to detect such small changes.
[0152] AuT Ag.sup.+ remediation from solution: Based on literature
data on other cyclic systems, the disclosed Au(I) systems have a
strong affinity to form "sandwich" adducts with heavy metals within
cyclic trimer rings. It is well established that these complexes
are luminescent due to the formation of cyclic dimer-of-trimer
units. The luminescence of this complex changes from red to green
upon formation of a "sandwich" complex with free Ag.sup.+ ions.
Taking advantage of this chemistry, studies were performed to
determine if this sensor could not only sense silver ions in
solution but whether it could also have the potential to
remediate/extract those ions from that solution. Such a sensor
could be utilized for both sensing and remediation applications.
Silver ions have been shown to be toxic for various biological
systems. Therefore, it would be highly advantageous to not only
sense their presence but also remediate them from the
environment.
[0153] Additionally, the simple and straightforward synthesis of
this sensor would be advantageous for its large-scale usage. To
begin, the sensitivity of silver ions at pH 4 and 6 were compared
in order to understand if the ligand played a critical role for
interacting with silver ions, or if the silver is exclusively
forming a sandwich adduct with the AuT. This study was done in the
absence of the CS polymer to minimize any background interference
from the polymer and also to obtain a clear picture of the
interactions of the trimer with the silver ions.
[0154] From the data in FIG. 22A, a clear relation between the pH
and sensitivity is noticed. There was a huge increase in
sensitivity of the complex by 2.5 times at pH 6 compared to pH 4.
Based on these data, one can conclude that the change in
sensitivity is due to deprotonation of the carboxylic acid at pH 6.
Therefore, the enhanced sensitivity clearly demonstrates
that--along with the formation of a sandwich structure--the
interaction of free Ag.sup.+ ions with the anionic ligand are
playing a vital role during the sensing process. Due to this, the
rest of the data collected in FIGS. 22B and 22C were done at pH 6.
FIG. 22B shows the addition of silver salt followed by addition of
KCl salt. Each point on the graph represents a new aliquot of the
same stock solution of AuT. The KCl was added after the addition of
silver ions to determine if silver precipitation by chloride would
affect the PL intensity of the green emission. As seen from the
data, KCl addition had no effect on the PL intensity up to about 5
ppm.
[0155] At higher concentrations of silver ions, the presence of KCl
does result in a significant decrease in the PL intensity of the
green emission due to the formation of AgCl. It is postulated that
this decrease in PL intensity occurs after 5 ppm because,
initially, the sandwich complex is forming, therefore the
"sandwiched" silver ions within the cyclic trimer units are
unavailable to react with the KCl. However, at higher
concentrations of silver ions, the excess silver ions are
hypothesized to interact with the carboxylated pyrazolate ligand,
based on FIG. 22A data, and are freely available to interact with
the excess of KCl--resulting in the quenching of the green PL of
the adduct. This data set clearly complements the pH-dependent
sensitivity of the sensor. FIG. 22C shows data from a similar
experiment except for the addition of KCl to the trimer before
addition of silver salt to determine how KCl would change the
sensitivity of the AuT when initially present in the medium. FIG.
22C shows clearly that even in the presence of KCl, the complex's
ability to sense silver was not affected, as indicated from the
control experiment (square dotted line in FIG. 22C). Comparing with
the control data, it is evident that the presence of salts like KCl
does not affect the complex's ability to sense free silver ions at
low ppm levels. This is a very important result for the application
of this sensor in water environments where the water medium is
known to contain different salts. These data show that even in the
presence of KCl, silver ions seem to preferentially interact with
the AuT complex. Therefore, it can be concluded that--regardless of
the order of addition of KCl to AuT--the sensor herein is still
able to remediate silver ions from aqueous solution.
[0156] Conclusions: In conclusion, a sensor has been developed that
is able to differentiate between Ag.sup.+ ions and AgNPs. One of
the great utilities of the sensor is to help nanoparticle
researchers to differentiate and understand if the toxicity of the
AgNPs is due to AgNPs alone, leaching of silver ions, or due to a
combination of both. Currently, differentiation of silver ions from
AgNPs directly in solution is not possible using any single
existing techniques. Differentiation of AgNPs from Ag.sup.+ ions is
vital since AgNPs are used in many commercially available consumer
products increasing the likelihood of human exposure. Not only was
the disclosed sensor able to differentiate between Ag.sup.+ ions
and AgNPs, but it was also able to sense the leakage of Ag.sup.+
ions from the AgNPs as well as remediate those ions from solution.
The remediation data not only showed the removal/extraction of
toxic silver ions from the medium but also demonstrated the first
step in making a reusable Ag.sup.+ sensor. Further investigations
should involve the application of this sensor in biological systems
to exactly understand the toxicity mechanism of AgNPs in vitro and
in vivo.
[0157] The following Example is intended to illustrate the above
invention and should not be construed as to narrow its scope. One
skilled in the art will readily recognize that the Examples suggest
many other ways in which the invention could be practiced. It
should be understood that numerous variations and modifications may
be made while remaining within the scope of the invention.
EXAMPLE
Example 1
Experimental
[0158] Materials. The gold precursor, gold
(tetrahydrothiophene)chloride (Au(THT)Cl), was synthesized by
following literature procedures (Uson, R.; et al., J. P. Jr. 1986,
Tetrahydrothiophene Gold (I) or Gold (III) Complexes, Inorganic
Syntheses, 26 (ed Kaesz, H. D), John Wiley & Sons,
Inc./Hoboken, N.J., USA. Ch17.). 3-methyl-1H-pyrazole-5-carboxylic
acid (ligand), cadmium nitrate, gadolinium acetate hydrate, and
europium perchlorate were purchased from Alfa-Aesar. CS low
molecular weight (85% deacetylated) was purchased from
Sigma-Aldrich as well as silver nitrate, thallium nitrate, mercury
nitrate, iron perchlorate hydrate, aluminum chloride hydrate,
manganese iodide, calcium hydroxide copper sulfate, cesium
hydroxide, potassium nitrate, cobalt nitrate, lead nitrate and
nickel chloride and zinc acetate. All chemicals were used as
received without further purifications.
[0159] Silver nanospheres stabilized in polyvinylpyrrolidone (PVP)
used in this study (0.02 mg/mL; 20-nm and 100-nm diameter) were
purchased from nanocomposix. The gold precursor,
Au(tetrahydrothiophene)Cl (Au(THT)Cl), was synthesized by following
literature procedure of Uson, R., et al. referenced above. Silver
nitrate, potassium chloride, low-molecular-weight chitosan (CS),
and 5-methyl-1H-pyrazole-3-carboxylic acid were purchased from
Sigma Aldrich and used without further purification.
[0160] Physical measurements. Steady state photoluminescence (PL)
spectra were acquired with a PTI QuantaMaster Model QM-4 scanning
spectrofluorometer attached with a 75-watt xenon arc lamp. The
xenon flash lamp was used to acquire the lifetime data. The direct
quantum yield was measured following a previously described method,
using an integrating sphere. pH measurements were made using a
Hanna instrument HI1053B pH probe. Electronic absorption spectra
were obtained with a Perkin-Elmer Lambda 900 double-beam UV-Vis-NIR
spectrophotometer. .sup.1H-NMR spectra were acquired in deuterated
dimethyl sulfoxide (DMSO-d.sub.6) on a 400 MHz Varian spectrometer
with a relaxation time of 6 seconds. Electrospray ionization mass
spectrometry (ESI-MS) data were acquired with a Thermo Finnigan LCQ
DECA XP Plus, using atmospheric pressure chemical ionization (APCI)
with a quadruple ion trap detector. Samples were then prepared in
50:50% water and methanol followed by addition of acetic acid to
facilitate the ionization. Fourier-transform infrared (FTIR) data
were acquired on a Thermo Scientific Nicolet 6700 FTIR
spectrophotometer equipped with a diamond attenuated total
reflection (ATR) attachment. Zeta potential measurements were
performed on a zetasizer nano ZS (Malvern Instruments).
[0161] In situ synthesis of Au.sub.3Pz.sub.3 in aqueous CS media.
Chart 1 (A) illustrates the formation of Au.sub.3Pz.sub.3 in
aqueous CS media. Although the synthetic procedure relevant to the
formation of Au.sub.3Pz.sub.3 in aqueous/aqueous polymer media has
been developed as described herein, the use of a polymer matrices
to immobilize/stabilize chemo-optical sensors is a well-known
technique. An excess amount of the pyrazole was transferred into a
reaction flask containing 1% wt/v CS polymer in deionized (DI)
water and stirred for 10 minutes. The pH of the solution was
adjusted with 1M NH.sub.4OH to be close to the pKa of CS
(.about.6.5) at which all measurements were conducted herein;
pH-dependent studies are ongoing. Then, a submolar quantity of
solid Au(THT)Cl was added directly into the ligand-CS aqueous
mixture and stirred for 2 more hours, resulting in a visually clear
(colorless) yet red-emissive Au.sub.3Pz.sub.3 solution. To
understand the role of the CS polymer, the same experimental
procedure was adopted for the synthesis of Au.sub.3Pz.sub.3 in
polymer-free DI water.
[0162] Synthesis of the gold trimer (AuT) sensor: A 10-mL sample of
dialyzed 1 wt % CS was added to a beaker. Then, 15 mg of
3-methyl-1H-pyrazole-5-carboxylic acid was dissolved in 1 mL of
methanol, added to the CS and allowed to stir for 10 min. After
stirring, a 240-.mu.L aliquot of 2 M NH.sub.4OH was added to
increase the pH to around 6.5. Lastly, a 5-mg sample of Au(THT)Cl
was added and the solution was allowed to stir for 45 minutes. Any
undissolved gold was centrifuged out, resulting in a clear
solution.
[0163] Preparation of solutions. Stock solutions with the required
concentrations of different heavy-metal salts were prepared using
Milli-Q DI water (18.2 MOhm-cm). For photoluminescence titration
studies, a known concentration of metal salt solution was added to
a 2 mL aliquot of the Au.sub.3Pz.sub.3 solution. PL spectra were
recorded before and after each addition.
[0164] While specific embodiments have been described above with
reference to the disclosed embodiments and examples, such
embodiments are only illustrative and do not limit the scope of the
invention. Changes and modifications can be made in accordance with
ordinary skill in the art without departing from the invention in
its broader aspects as defined in the following claims.
[0165] All publications, patents, and patent documents are
incorporated by reference herein, as though individually
incorporated by reference. No limitations inconsistent with this
disclosure are to be understood therefrom. The invention has been
described with reference to various specific and preferred
embodiments and techniques. However, it should be understood that
many variations and modifications may be made while remaining
within the spirit and scope of the invention.
* * * * *